Originally Posted by
Anoiktos
In addition to what above posters have said, there are some general things to remember as any tank:
1) Positioning. Always be facing the mobs you're fighting, or you can't dodge. And if you can't dodge, you're taking 20-40% more physical damage.
2) Positioning. Keep enemies where they aren't going to hurt your allies with incidental fire. Juggernauts in Zul'aman? Keep them away from the range so the healer doesn't have to heal accidental earthquakes on even more targets.
3) Control. Your job as the tank is twofold: To minimize damage to your allies, and to minimize damage to yourself. The first job here is an important one that it sometimes lost in the interim; due to the way healing mechanics work nowadays, it is easier for your healer to heal just you than to try to waste inefficient heals on other targets so that they can get back to pinging you with their efficient heals.
4) Control. Share the job of damage mitigation. Encourage your allies to crowd control. If they whine about it, and you're in a heroic, kick them unless they're the healer. If they whine about it, they're the healer, and they're struggling to keep you up, kick them anyway. Crowd control may not be 'fast', but it's almost ALWAYS faster than wiping.
5) Control. Know what to interrupt, when. Remind others to interrupt if they aren't. Know who has what interrupts with what cooldowns. Use something like recount and check the 'interrupts' and 'deaths' categories; DPS and healing meters are usually irrelevant. (Unless your DPS are pulling 3k in heroics on bosses, in which case there's usually something wrong.)
6) Cooldowns. Every tanking class has cooldowns. The trick is to know when to use them. If you have a short cooldown, like barkskin, use it whenever it's convenient. Pulling multiple mobs? Barkskin. Getting low on health? Barkskin. If your barkskin is off cooldown and you're taking interesting amounts of damage, you're wasting your healer's mana. Longer cooldowns are best saved for panic conditions; you've got an extra mob? The crowd control failed? The boss is using an ability? Your healer's OOM? Your healer's standing in the fire? Blow cooldowns.
7) Awareness. This is perhaps the most noticeable difference between a good tank and a bad tank, at equal gear levels. A good tank notices when the healer's under attack. A good tank knows the encounter, and will understand when it's difficult for the healer to heal them. A good tank understands that sometimes stupid DPS stand in fire, and the healer, being less pragmatic than you, will try to heal them instead of letting them die like the chumps they are. Use your abilities appropriately. Faerie fire or taunt the mob attacking the healer. Feral Charge the incoming pat before one of the DPS body pulls (but be careful to turn to face your enemies ASAP so they don't hit you from behind), and be prepared to blow cooldowns. A good tank knows when their healer is low on mana.
8) Debuffs. Keep demoralizing roar up. Always. That's 10% damage you're not taking, and 10% (or more, due to the way healer mana efficiency works nowadays!) mana the healer isn't wasting.
9) Buffs. Keep Pulverize up. That's 9% more crit for you, which means 4.5% more of a chance per hit that your Savage Defense procs, and quite a bit more threat. Keep Mark of the Wild up. Make sure that your warrior or DK use their agi/strength buffs. Make sure your priest or warrior use their stamina buffs. Make sure your paladin uses their might buff. Know what buffs different classes have; they act as power multipliers, creating a nice buffer between you and the grave. If you're having trouble, invest in some agi/stam food - fish up some eels from the pools in Uldum (no, you don't need a high fishing skill to fish from pools, and as a bonus it helps your guild's achievement) and pass them on to a guild cook for 90 extra stam/agi.
10) Cooldowns, Part II: Berserk is an amazing cooldown. For the duration (and the cooldown isn't that long), you're doing 3x15-30k damage per mangle - every global cooldown. This means the mobs die faster, it means your savage defense is almost always up, and it means no one is pulling aggro from you. It also makes you feel like a god.
11) Know the other roles, know the other classes. Play a healer. Play a DPS. Learn what classes have what CC, and what CC applies to what targets. Be bossy, but accept corrections with a smile and always be ready to learn new things. Every role you play teaches you different things about the mobs you fight, and different things about what you wish your tank was doing - which means what you can do to improve as a tank.
12) Be patient. Some people are idiots. Some people just don't know what they can do. Some people are inattentive. Things happen. People die. They get back up again, because this is WarCraft, and not reality. Generally, being patient and understanding goes a long way, but sometimes people are just rude, annoying, and insufferable. If it gets to be too much, apologize to your group, honestly point out what you think is going wrong, preferably without being snide, and leave group. 90% of the time you won't get a debuff, and the other 10% of the time you can go grab a drink and relax for the duration. Don't do this to punish them - frankly, they'll get another tank in a couple of seconds.
13) Try again. You won't always succeed; mechanics in Cataclysm heroics are not like those in WOTLK, the tank (unless he/she's REALLY geared, and even then...) can't carry a terrible group through all the encounters. Healers have to know who and what to heal (dispel the damn lash on the panther boss), DPS have to understand how to interrupt and when not to stand in fire (Especially on venoxis), because you only have one interrupt per 10-60 seconds. (I always talent for 10, but it's preference; I find the ability to interrupt mobs saves me a lot of damage in the long run.) You can't really control these factors, so if you're pounding your head against the brick wall of other people's failings, don't insult them, just quietly and politely state what you think is going wrong and if it doesn't improve, leave the group and find another. Some people can't (or more likely won't) be helped.
The key here is: All of these directly or indirectly affect your survivability. Survivability isn't stats, it's stats + context. Manipulating your context to minimize incoming damage multiplies the work your stats do, and can turn you from a well-geared tank to an amazing tank.