Basic Information
Blood is now a tank spec. Yep.
DPS: Removed, RIP.
Tanking: Blood tanking relies primarily on having a large health pool. Vampiric Blood, Rune Tap and Will of the Necropolis all rely on having a big health pool. Heart Strike, Death Strike and Rune Strike are the main single target threat abilities. Heart Strike, Blood Boil, Death and Decay are the main multi-target threat abilities.
Talent Builds and Rotations
Main Stats
Maintaining a balanced stat sheet is important. You want a good amount of stamina, mastery, avoidance, hit and expertise. You need to stamina to both survive and heal yourself. Mastery also increases the effectiveness of your main self heals by providing a physical absorb shield from Death Strikes. Avoidance reduces total damage taken and thus total healing required. Hit and Expertise make sure your Death Strikes land when they need to.
Example Specs
How to Not Die
Single target threat is generally not an issue due to Vengeance stacks, therefore the primary consideration for a tank is survival.
How does the Death Knight survive?
Diseases now reduce the physical damage you take from infected enemies. They now apply both the Thunderclap and Demoralizing Shout (with talent) debuffs. Make sure these are up 100% of the time on any dangerous enemies. Incidentally, they also increase your threat output, so why not?
Cooldowns are relatively self-explanatory. You activate a cooldown, your chances of survival increase.
Death Strike - This melee ability will heal you for 7% of total health or 15% of the incoming damage within the last 5 seconds, whichever is greater, and as a Blood DK it will also shield you for a % of the amount healed based on mastery. While you will cause a substantial amount more damage/threat by using Death Runes on Heart Strike, you should keep in mind that you are trading your healers' mana for that damage/threat.
Rune Tap - Heals you for 10% of your total health. With the glyph, this will also heal your party for 5% of total health (which is a respectable amount). With a 30 second cooldown, do not save this for a rainy day, especially considering that you will have Will of the Necropolis proccing when you do need it.
Anti-Magic Shell - Absorbs 75% of all incoming magic damage for 5 seconds up to 50% of your total health in total absorption. This also prevents most magic debuffs from being applied to you. Time it well. A good DK will time it to eat a damaging spell, a great DK will time it to eat a nasty spell with a nastier debuff (read: meteor slash).
Bone Shield - This self-buff will keep a 20% damage reduction effect on you for the first few attacks of a fight. Always make sure to refresh this during and between fights, as there is only a 1 minute cooldown.
Vampiric Blood - Increases your current and maximum health by 15% and increases all incoming heals by 25%. Activate this regularly, it will increase your Death Strike heals and shields in addition to any heals from your healers.
Dancing Rune Weapon - Increases your chance to parry by 20% and also summons a weapon to attack your enemies. Note that this ability costs 60 Runic Power to activate!
Lichborne - Subspeccing in Frost gives you this ability to turn undead for 10 seconds, granting fear/charm/sleep immunity but more importantly the ability to be healed by Death Coils (both by your own and your fellow DKs').
Icebound Fortitude - Stun immunity and 50% damage reduction. This is the big cooldown. Use it when you're in big trouble.
Empower Rune Weapon - Resets all your runes. A nice threat tool, but nicer still is the fact that you can Death Strike twice in a row right afterward for some massive healing.