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As said before all credit for this guide goes to Ashes from Malganis. The original version of this guide can be found here.

Ashes’s Death Knight Tanking Guide
Updated 8/27

1. The Basics
1.1 Gameplay
1.1.1 Rune System
1.1.2 Runeforging
1.2 Skills
1.3 Talents
1.4 Specs
1.5 Rotation
2. Advanced Training
2.1 Stat priorities
2.2 Enchants, Glyphs, and Runeforges
2.3 Dungeons & Raids
3. FAQs
4. Acknowledgments
5. Links

Foreword:

My Death Knight's name is Rhnea. Generally, most people refer to me by my pally's name Ashes. I have played all the tanking classes in raiding environments. That said, I have only raid tanked on my Death Knight on the server Mal'Ganis. DK Tanking is a sort of proactive tanking. We have 2-3 cooldowns and Blade Barrier. All these are activated by either pressing a button or using all of the blood rune slots. This means you have to know what to expect and when to expect things so you can minimize the incoming damage, as compared to other tanks who are built to take damage and press oh-@##@ buttons when they need.

Abbreviations Used:
Avoidance: Dodge\Parry\Miss
DPS: Damage Per Second or Damage Dealing Class
Mitigation: Damage reduction (i.e. spell damage reduction and armor)
GCD: Global Cooldown
DoT: Damage Over Time
AoE: Area of Effect
HoT: Heal Over Time
RP: Runic Power
IT: Icy Touch
PS: Plague Strike
HS: Heart Strike
SS: Scourge Strike
BB: Blood Boil
HB: Howling Blast
HC: Hungering Cold
Ob: Obliterate
UB: Unholy Blite
DnD: Death and Decay
AotD: Army of the Dead

1.0 The Basics

I just would like to mention that I don't intend to tell people how to play. This guide is meant to be a reference and give you a good foundation on how to play. By all means please feel free to post with any ideas you may have. Most people like to talk about specs since it is one of the most dynamic and influential things in this game. Also, please let me know if you don't think something is accurate or I don't do something justice. I will happily look over things again. Happy Tanking!

1.1 Gameplay:

We are pretty in line with the other tanks as far as incoming damage. We are a little squishier at times, but that's what our cooldowns are for. With some practice and quite a bit of insight you can do some amazing things as a Death Knight tank. The crux of the Death Knight though is the constant need to pay attention to all your details in order to maximize your tanking ability. I won't lie, this can become overbearing at times, but with a certain finesse you can keep most situations on lock down.

1.1.1 The Rune System:

The Death Knight's ability system works off a combination of all 3 pools. The Death Knight in its current state has 6 runes: 2 Blood, 2 Frost, and 2 Unholy. Basic abilities use a rune or a combination of runes. Some, are free of cost, but most use runes. As you use runes you build runic power. For each single rune ability you generate 10 runic power, and all multi rune abilities generate 15.The first rune of each Blood, Frost, and Unholy recharges in 10 seconds, while the second is on an 8.5 second cooldown due to latency purposes so that’s essentially 10 secs too. Sometimes, you can regen them faster depending on your talents. Once you have runic power you can then use other abilities such as Death Coil. These abilities are usually a plus and give you a chance to have a choice in fillers. Also, as you use abilities you will start to debuff the target with diseases. Which diseases and how many depends entirely upon your spec. The more diseases you keep up the more additive damage you will do with certain abilities i.e. death strike.

1.1.2 Runeforging:

Runeforging is a pretty simple system. It's a cross between poisons and enchants. With runeforging you can enchant your weapon with a permanent weapon aura. This aura does not work with weapon enchants, however, it does work with temporary enchants such as oils and windfury. You can change your runeforge enchant at any runeforge, for your convenience, in Ebon Hold. More in detail about what to use later.

1.2 Skills

Blood:

Blood Boil
1 Blood, Instant Cast
Causes any of the Death Knight's diseases on the target, and all enemies within 30 yards of the target to painfully erupt, dealing X to Y Shadow damage. Deals additional damage to targets afflicted with Frost Fever or Blood Plague.

This is your new AoE snap agro unless you’re frost. This does a good deal of damage to help get you started, but make sure you spread your diseases first.

Blood Tap
X% health, Instant Cast, 1 Minute Cooldown
Immediately activates a Blood Rune and temporarily converts it into a Death Rune. Death Runes count as a Blood, Frost, or Unholy Rune This rune counts as a Blood, Unholy, or Frost Rune. Lasts 20 sec.

It's nice for those times when you're just short 1 rune for obliterate or Howling Blast. It gives you a quick opportunity to take advantage of the all out moments. Some people will use this also after your first opener set to get another rune for a blood boil.

Dark Command
30 yd, Instant Cast, 8 sec Cooldown
Commands the target to attack you, but has no affect if the target is already attacking you.

Basic taunt

Death Pact
40 Runic Power, Instant Cast, 2 min cooldown
Sacrifices an undead minion, healing the Death Knight for 40% of your maximum health. This ability cannot critical.

Nice ability to regain some health and it works on all your undead minions even AotD.

Forceful Deflection (Passive)
Increases your Parry Rating by 25% of your total Strength.

It makes our str (source of attack power) even more useful outside of dps.

Pestilence
1 Blood, Instant Cast, Melee Range
Spreads existing Blood Plague and Frost Fever infections from your target to all other enemies within 10 yards.

This is your ability to spread your diseases and get all the mobs debuffed. With the glyph of disease this is your auto refresher on diseases. This ability doesn’t cause any agro other than allowing your diseases to tick on other mobs.

Strangulate
1 Blood, 30 yd, Instant Cast, 2 min cooldown
Strangulates an enemy, silencing them for 5 sec.

One of many abilities you can use to silence an enemy; however, this is one of the only few that can be performed at range. It also has the nice added effect of shadow damage when the silence is done.

Frost:

Empower Rune Weapon
Instant cast, 5 min Cooldown
Empower your rune weapon, immediately activating all your runes and generating 25 runic power.

Basically it's the prep button for when your group is going to pop all their cooldowns or if you just want to get in a bunch of attacks for a threat boost..

Horn of Winter
Instant Cast, 20 sec cooldown
The Death Knight blows the Horn of Winter, which generates 10 runic power and increases total Strength and Agility to all party or raid members within 30 yds by X. Lasts 2 minutes

This is a great thing to cast before a fight and during a fight. It boosts a lot of your avoidance stats and gives you some extra runic power. In fact, I keep it macro'd to my Scourge Strike so when I'm smashing that button I'll cast it repeatedly, and boost my rp and stats. I also have this macro'd to my rune strike since RS has no GCD. P.S. Good idea not to have all your DK's glyph Horn since if even one of them has it it prevents all DKs from being able to cast this while their Horn is up.

Frost Presence
1 Frost Rune, Instant Cast
The Death Knight takes on the presence of frost, increasing total health by 6%, armor contribution form cloth, leather, mail, and plate by 60%, and reducing damage taken by 5%. Increases threat generated. Only one presence may be active at a time.

The tanking presence. It increases mitigation to magic and physical damage. It also raises your threat. Oh and YAY more health!! Keep in mind this only considers your base slots not trinkets, rings, and necks.

Icebound Fortitude
20 Runic Power, Instant Cast, 2 min cooldown
The Death Knight freezes her blood to become immune to Stun effects and reduce all damage taken by 20% plus additional damage based on Defense for 12 sec.

This is basically the Shield Wall of DK's. It's our best damage reduction ability. On top of that it only has a 1 minute cooldown to boot. This makes defense rating more essential for DK tanking, but you can glyph in the extra 30% with the glyph of IBF

Obliterate
1 Unholy 1 Frost, Melee range, Instant Cast, Requires Melee Weapon
A brutal instant attack that deals 80% of weapon damage plus X, and an additional 12.5% bonus damage per disease, but consumes the disease.

This is your threat spam attack for blood. This ability is also useful for frost when HB is on cooldown. Make sure you spec Annihilation if you do use this ability to prevent it eating all your diseases.

Rune Strike
20 Runic Power, Next Melee, Requires Melee Weapon
Instantly strikes the target for 150% weapon damage plus X. Only useable after the Death Knight dodges or parries. Can't be dodged, blocked, or parried. Does 150% threat.

This is the revenge for DKs. It is mainly a tanking ability and it has a higher amount of threat. Since it's next melee you can just queue it up while you're continuing with your rotation. Lots of DKs will macro this with their abilities or at least Horn of Winter to continually cast it whenever it’s up.

Unholy:

Anti-Magic Shell
20 Runic Power, Instant Cast, 45 sec cooldown
Surrounds the Death Knight in an Anti-Magic Shell, absorbing 75% of the spell damage dealt by harmful spells (up to a maximum of 50% of the Death Knight’s Health) and preventing application of harmful magical effects. Damage absorbed by Anti-Magic Shell energizes the Death Knight with additional runic power. Lasts 5 sec.

One of the most amazing abilities death knights have against casters. It also prevents applications of magical debuffs too. This means that fights where magical debuffs are applied you have a great defense, and you don't even have to move.

Death and Decay
1 Blood 1 Frost 1 Unholy, 30 yd Range, Instant Cast, 30 sec cooldown
Corrupts the ground targeted by the death kngiht, causing X damage every sec that targets remain in the area for 10 sec. This ability produces a high amount of threat.

A great AoE tanking ability, the fact that you can cast it at range makes it a great AoE for those times when your mages want to go crazy and you just can't get in range quick enough.

Death Coil
40 Runic Power, Instant Cast, 30 yd range
Fire a blast of unholy energy, causing X Shadow damage to an enemy target or healing X damage from a friendly Undead target.

A great ability to use as a filler to give yourself a little more threat. The wording on the heal portion of it makes it confusing, but it seems to be a nice way to heal yourself (while in licheborne form), or your ghoul.

Death Grip
30 yd range, Instant Cast, 35 sec cooldown
Harness the unholy energy that surrounds and binds all matter, drawing the target toward the death knight and forcing the enemy to attack the death knight for 3 sec.

One of the abilities you can have fun with. It is literal a pull mechanism. You pull the target smack in front of you, and if you're smart you'll cast icy touch or death coil on it as it's coming down.

Death Strike
1 Unholy 1 Frost, Melee Range, Instant Cast, Requires Melee Weapon
A deadly attack that deals 75% weapon damage plus X and heals the death knight for 5% per number of disease on the target.

A great ability to give yourself a small heal.

1.3 Death Knight Talents

These are the talents that I have found more focused on tanking. The other talents tend to give you more dps, which is more threat, but I don't think they need to be discussed within this thread since this is quite a bit to digest in the first place. Also, it needs to be mentioned that the different death rune abilities prove to be handy when you want to get more into your rotation as far as damage or clickies go.

Blood:

Blade Barrier x/5
Whenever your Blood Runes are on cooldown, you gain the Blade Barrier effect, which decreases damage taken by 1/2/3/4/5%.

This is one of those talents that all tanks must get. It reduces your damage intake by 5% and all you have to do is just burn the blood runes. This doesn’t work if they’re just sitting as death runes though. You actually have to use those rune slots to activate the talent.

Rune Tap x/1
1 Blood Rune, Instant Cast, 1 minute cool down.
Converts 1 Blood Rune into 10% of our maximum health.

Great little self heal ability, it's similar to the warrior's last stand, and it's a self heal every minute or 30 sec depending on your talents.

Improved Rune Tap x/3
Increases the health provided by Rune Tap by 33/66/100% and lowers it's cooldown by 10/20/30 secs.

See above.

Spell Deflection x/3
You have a chance equal to your Parry chance of taking 15/30/45% less damage form a direct damage spell.

Another source of spell damage mitigations making us even better at being caster tanks. Keep in mind this doesn’t affect AoE attacks such as breaths (for the most part).

Veteran of the Third War x/3
Increases your Strength and stamina by 1/2/3% and your expertise by 2/4/6

Buff to stam and str and adds a little to expertise.

Mark of Blood x/1
1 Blood, 30 yd, Instant Cast, 3 min cooldown
Place a Mark of Blood on an enemy. Whenever the marked enemy deals damage to a target, that target is healed for 4% of its maximum health. Lasts for 20 seconds or up to 20 hits.

Nice little ability to help you get topped off can be useful to help out when you're not Main Tanking something too.

Vampiric Blood x/1
1 Blood, Instant Cast, 2 min cooldown
Temporarily grants the Death Knight 15% of maximum health and increases the amount of health generated through spells and effects by 35% for 20 sec. After the effect expires, the health is lost.

A great way to increase the healing done on you, and increase your health pool for the moments when you know you're going to need it.

Will of the Necropolis x/3
Damage that would take you below 35% is reduced by 5/10/15%. This effect cannot occur more often than once every 15 sec and cannot be triggered by damage which deals less than 5% of your health.

This ability will increase your effective health pool by 15% every 15 sec, but since it has a cooldown it’s utility is reduced significantly.

Heart Strike x/1
1 Blood, Melee Range, Instant Cast, Requires Melee Weapon
Instantly strike the target and his nearest ally, causing 50% weapon damage plus X, total damaged increased by 10% for each of your diseases on the target.

This ability is a nice way to get some multiple mob damage, and it does a decent amount of damage. This is your Blood Strike replacement.

Frost:

Improved Icy Touch x/3
Your Icy Touch does an additional 5/10/15% damage and your Frost Fever reduces melee and ranged attack speed by an additional 2/4/6%.

Reduces melee and ranged attack speed meaning you won't be hit as often. Plus, a little extra damage on your Icy Touch.

Runic Power Mastery x/2
Increases your maximum Runic Power by 15/30.

Gives you a little more to work with in the way you sink your Runic Power.

Toughness x/5
Increases your armor value from items by 2/4/6/8/10% and reduces the duration of all movement slowing effects by 6/12/18/24/30%.

Basic tank increases armor talent with the bonus of decreasing movement impairment.

Lichborne x/1
Instant cast, 3 minute cooldown
Draw upon unholy energy to become undead for 15 sec. While undead, you are immune to Charm, Fear and Sleep effects.

It's a neat ability to break fear and a few other CC abilities some mobs have. Also, you can heal yourself with deathcoil while in this form.

Annihilation x/3
Increases the critical strike chance of your melee special abilities by 1/2/3%. In addition, there is a 33/66/100% chance that your Obliterate will do its damage without consuming diseases.

Gives you more freedom to use other abilities since you won't have to refresh your diseases.

Frigid Dreadplate x/3
Reduces the chance melee attacks will hit you by 1/2/3%

A base chance for melee to miss you. Quite handy since most all mobs melee.
Merciless Combat x/2
Your Icy Touch, Howling Blast, Obliterate and Frost Strike do an additional 6/12% damage when striking targets with less than 35% health.

Just a nice little umph for when warriors and such are execute spamming.

Hungering Cold x/1
40 Runic Power, Instant Cast, 1 min cooldown
Purges the earth around the Death Knight of all heat. Enemies within 10 yards are trapped in ice, preventing them from performing any action for 10 sec and infecting them with Frost Fever. Enemies are considered Frozen, but any damage other than diseases will break the ice.

It infects all the mobs within 10 yards with frost fever giving your Howling Blast a nice boost to up your AoE tanking in instances plus it gives you a semblance of CC when the mobs are freezable. The usefulness of this ability is negligible in PvE.

Frost Aura x/2
While in Blood Presence or Unholy Presence, you retain 5/10% health from Frost Presence, and damage done to you is decreased by an additional ½% while in Frost Presence.

Let’s you keep your health regardless of presence, and you increase your damage reduction when tanking.

Unbreakable Armor x/1
1 Frost, Instant Cast, 2 minute cooldown
Reinforces your armor with a thick coat of ice, reducing damage from all attacks by X and increasing your strength by 25% for 20 sec. The amount of damage reduced increases as your armor increases.

This is an extra damage reduction clicky for you. This really does a nice number when AoE tanking.

Acclimation x/3
When you are hit by a spell, you have a 10/20/30% chance to boost your resistance to that type of magic for 18 sec. Stacks up to 3 times.

Most tanks don’t waste their time with this ability since it’s so iffy, and it’s utility is quite marginal.

Guile of Gorefiend x/3
Increases the critical strike damage bonus of your Blood Strike, Obliterate, Howling Blast and Frost Strike abilities by 15/30/45% and increases the duration of your Icebound Fortitude by 2/4/6 sec.

Basically this will allow you to keep icebound fortitude up most of the time. Oh and more damage aka threat, whee.

Howling Blast x/1
1 Unholy 1 Frost, 20 yd range, Instant, 8 sec cooldown
Blast the target with a frigid wind dealing X to Y Frost damage to all enemies within 10 yards.

This is your Oblit replacement when it’s not on cooldown. On top of that with the glyph it will infect all hit with Frost Fever.

Unholy:

Anticipation x/5
Increases your chance ot dodge by 1/2/3/4/5%

Basic tank +dodge talent.

Morbidity x/3
Increases damage and healing of Death Coil by 5/10/15% and reduces the cooldown on Death and Decay by 5/10/15 sec.

This is a nice way to get your AoE threat up. Also, it does a nice number for single target since you can Death Coil more often.

Epidemic x/2
Increases the duration of Blood and Frost Fever by 3/6 sec.

It gives you the opportunity to use a couple more damaging attacks (i.e. Scourge Strike/Blood Strike) Before you have to refresh your diseases.

Unholy Command x/2
Reduces the cooldown of your Death Grip ability by 5/10 sec.

Lowers your cooldown on your death grip and who doesn't like to pull people around.

On a Pale Horse x/2
You become as hard to stop as death itself. The duration of all Stun and Fear effects against you is reduced by 10/20% and your mounted speed is increased by 10/20%. This does not stack with other movement speed increasing effects.

This ability is a nice ability, but it tends to be a more PvP ability. However, if you find yourself with extra points… put them elsewhere. Don’t fall into the temptation!

Unholy Blight x/1
Causes the victims of your Death Coil to be surrounded by a vile swarm of insects, taking 20% of the damage done by Death Coil over 10 sec.

This is a nice way to boost your threat without having to do anything extra.

Magic Suppression x/3
You take 2/4/6% less damage from all magic. In addition, your Anti- Magic Shell absorbs an additional 8/16/25% of spell damage.

Decreases your spell damage intake. It has proven extremely useful in fights where you are fighting an elemental, or a dragon since a lot of their damage is magical damage.

Anti-Magic Zone x/1
1 Unholy, Instant Cast, 2 minute cooldown
Places a large, stationary Anti-Magic Zone that reduces spell damage done to party or raid members inside it by 75%. The Anti-Magic Zone lasts for 10 sec or until it absorbs (10,000 + 2*AP) spell damage.

An AoE cover for you and your friends. It's centered around you. It'll be nice for fights where there's plenty of AoE damage and all around spell Chaos. This can be helpful even when you aren't tanking. You can toss this down to help mitigate damage against anyone who stands in this zone.

Bone Shield x/1
1 Unholy, Instant Cast, 2 min cooldown
The Death Knight is surrounded by 4 whirling bones. While at least 1 bone remains, you take 20% less damage from all sources and deal 2% more damage with all attacks, spells, and abilities. Each spell or attack that lands consumes 1 bone. Lasts 5 minutes.

Damage mitigation and extra damage. Only good/bad thing is each bone is consumed with each successful attack on you. It's been theorized you can keep this up for an entire minute if you have a high enough avoidance. AoE's do not consume bones

Keep in mind that blizzard has emphatically expressed that their full intention is to make all of our trees will be tank viable. It's just a matter of how much you're willing to sacrifice and how well you play your class and spec.
On a note of sarcasm: Go figure you have to know how to play to be able to main tank.

1.4 Spec Suggestions
Please see if you need templates.

As a note from my experience Frost seems to be the more undergeared tanking tree, unholy tends to mitigate and do more magical damage, while blood is higher on stat allocation. This being said. I think when you're heading into ToC25 or 10 Blood or Frost are your better choices.

1.5 Rotations
I haven't been able to do the number crunching but for the most part the opener for most tanking situations will be...

Disease Application:
Rotations as far as they go have started to become like attack priorities after the initial pull. Once you have started the pull and got in your first set of attacks death runes come into play and that means you have a lot more to play with.

General Pull goes like...
IT ---> PS ---> Pestilence ---> DnD or HB ---> BS/BB

You can switch IT and PS but really you should be far enough to get the IT off. Some people are really keen on using PS first then by all means this is a guide. However, realize that in the time you've hit it as it's running (or flying at you cause of death grip) you can have your next attack up from GCD.

After the initial attack you should SS, Oblit, or HB depending on your spec whenever you can, and the mob is debuffed accordingly. The only thing I caution is make sure you're always keeping in mind your blade barrier. If you can get your blood runes to be used consecutively, and then used together as death runes it's probably the easiest route. If you have a mind for the runes you could always use the runes in an alternating pattern. The latter gives a much more consistent lock down on blood rune use. Remember though BOTH blood runes must be used whether as Death Rune or Blood for Blade Barrier to be active.

2. Advanced Training
2.1 Stat Priorities

The first and major priority for tanks is the defense cap. This should be your first and primary goal. For level 80 you need 540 defense (that's 688 defense rating) total at all times when tanking level 83/boss mobs. If you have anything less than this there is a good chance you will be crit by the boss's physical attacks. In fights where it is all spell damage this can go out the window. Also, it is noteworthy that when you do get 540% defense you effectively added another 10% avoidance to your sheet because the crit bosses have and the defense bonus itself are converted to a miss chance.

After this it can be taken down this path or something similar to:
Stam/Str
Dodge/Parry
Hit/Expertise
Crit/Agi
AP

Stam/Str are a bigger priority than the rest. You need a nice little cushion for the incoming damage that will be coming in. And though this may not be the best argument, but healers tend to see a decent amount of health so that they don't lose faith in their tank's ability to handle the situation. Strength will give you more threat, but with our forceful deflection we will be able to parry more so this proves to be even more useful. So this is why Str is so far ahead of AP on the priority list.

Hit/Expertise are great tools to help you push that DPS out to get more threat, but your main priority is tanking, and although being a threat rocket is great if you can't survive the fight and give healers something to work with the fight will not go well. I do like these stats don't get me wrong, but in the grand schema of things it isn't as big priority. Plus, you seem to get these as time moves on pretty easily. The same goes for Crit/Agi/AP

Here I would like to mention that there are diminishing returns for dodge/parry rating. So if you have a high rating you should start looking at other stats at this point, or at least the other avoidance. For instance, if you like to stack parry once you notice your parry rating is getting less effect. Dodge and parry have been equalized now, and it should be easier to pick your avoidance stat now. If one seems significantly lower you can start stacking the other, but remember parry increases your attack speed which then can cause the boss to parry. This can then cause you to
2.2 Runeforges, Enchants, and Glyphs

Runeforges:
As far as Runeforges go if you are tanking you'll want either
Rune of the Stoneskin Gargoyle (two-handed only) now grants 25 Defense and 2% Stamina.
or
Swordshattering: +4% Parry and reduces disarm affects by 50% on a 2h-weapon
(I would easily pick these over any Weapon Enchants until something better comes along.)

Enchants:
Head - Arcanum of the Stalwart Protector (Argent Crusade - Revered) +37 Stam and +20 def rating
Shoulder - Greater Inscription of the Pinnacle (The Sons of Hodir - Exalted): +20 dodge rating and +15 def rating
or Master's Inscription of the Pinnacle (Inscriptioner Only) - +52 dodge rating and +15 def rating
Cloak: Titanweave: +16 Def Rating
or Mighty Armor: +225 Armor
Chest: Powerful Stats: +10 to all Stats
or Greater Defense: +22 defense rating
Bracers: Greater Stam: +40 Stam
or Expertise: +15 Expertise
or Major Defense: +12 def rating
Gloves - Armsman: +2% Threat and 10 Parry Rating
or Precision: +20 hit rating
or Expertise: +15 expertise rating
or Heavy Borean Armor Kit: +18 stamina
Legs - Frosthide Leg Armor: +55 stam and +22 Agility
Feet: Greater Fortitude: +22 stam
or Tuskarr's Vitality: +15 Stam and +8% movement
Rings (Enchanters Only) Stamina: +24 stam
Weapon: +50 Stamina
or Blade Ward (Blade Warding increases your parry rating by 200 and inflicts 600 to 800 ddamage on your next parry. Last 10 sec.)
or Blood Draining (When you fall below 35% health, Blood Reserve restores 360 to 440 health. Lasts 20 sec and stacks up to 5 times.)

Now you can pick up different enchants if you're comfortable with our mitigation, but these are the prime ones orientated toward tanking. If you're defense capped then It would be best to go for the other enchants.

Glyphs:
Major:
Anti-magic Shell: Adds 2 seconds to AMS.
Bone Shield: Adds 2 extra bones to your Bone Shield
Death and Decay: +20% damage.
Disease: Your Pestilence ability now refreshes disease duration on your primary target back to their maximum duration.
Howling Blast: Your Howling Blast ability now infects your targets with Frost Fever.
Rune Tap: Heals your party for 10% of their max health
Unbreakable Armor: Increases the amount of damaged absorbed by 20%
Vampiric Blood: +10 seconds.

There are different combination for glyphs. You really need to pay attention to your spec to make sure you have the ones maximizing your threat and survivability. For instance as Blood: Death Strike, Vamp Blood and something else, Unholy: Scourge Strike, Bone Armor, and something else, Frost: Unbreakable Armor, Howling Blast, and some other thing. All these things you want to keep in mind, and there are different glyphs for each spec these are just suggestions to help you get started out.

Minor:
Blood Tap: Your blood tap no longer causes damage to you.
Death's Embrace: Gives 20 runic power when you use Death Coil to heal.
Pestilence: Increases the radius of Pestilence by 5 yards.
Glyph of Raise Dead: Gives 20 RP when raising a ghoul
Horn of Winter: Increases duration by 1 minute.

I find that Pestilence is a must. The other 2 are a little more liberal as choice, but Death's Embrace and Raise Dead are nice runic power ones.

2.3 Dungeons & Raids
As far as heroics go you'll be set to tank it with around 510 defense comfortably. All the bosses are just 2 levels above you at that point. You shouldn't have too spikey of damage either. Also, if you have 21k+ health you'll be sitting easy. Just make sure to be on top of your cooldowns and try to minimize incoming damage as best possible with IBF and such. I tend to pop IBF right before a swarm of mobs is coming on me.

As for raids:
For 10 and 25 mans (t7 content) it's a little bit more taxing. You'll need 540 defense and a good health pool, 23k unbuffed is probably optimal. In addition I wouldn't recommend going in with less than 40% combined dodge/parry. If you're close to it you should be fine.

For t8 content all the above apply, and you should have about 30k health unbuffed. If you’re having trouble with this I would suggest the blood tree to cushion your health pool. As far as avoidance goes 55% Dodge + Parry should be good.

Something cool to note: You can use Army of the Dead as an oh snap button on raid bosses because the zombies will not taunt raid bosses, but they will taunt regular bosses. So long as you have a Skull for the level of the target you're safe to use AotD.

3. FAQ (Frequently Asked Questions)

1. What spec is best for tanking?
As far as normal and even heroic dungeons go, any spec should be fine. Death Knights by design have been given the ability to tank in any of their trees so long as they have a good knowledge of their skills, and can play their class. As for raiding it is highly recommended to get the bottom 3 mitigation/avoidance talents maxed out before you plan your raiding spec. Each tree has its quirks and can all tank in raid situations. The gear is just what will really make or break you at that point.

2. Do we need to have 102.4% Avoidance to prevent Crushing Blows?
No you don't need to get high avoidance to avoid crushing blows anymore. They have been taken out for mobs 3 levels higher than you; however, it still exists for mobs 4+ levels higher than you to prevent you from taking on anything out of your league.

3. Do Death Knights compare well/scale well compared to the other tanking classes?
I have had no problems tanking 25 mans and 10 man pugs as the MT. So I would say we're in a good disposition. Our threat and mitigation are pretty nice now, and with the amount of clickies we get it's pretty job imo.

4. Acknowledgements
Venia, Naito and the rest of the DeathKnight.info crew for their input.

5. Links
Tanking Spreadsheet for those theorycrafters. Thanks Tantlin

Reference Compilation.

Much more comprehensive FAQ:

(As said before all credit for this guide goes to Ashes from Malganis. The original version of this guide can be found here.)