Tanking is vital to any instance/raid, and with some of the 10 men stuff going 5 men on 1.10 the work of a sole tank will be largely asked for.
There's a lot of guides about tanking on the net, o'course.
So, that's they way aha aha I do it.
Stats:
Obviously, Stamina is the primary stat, followed by Strength and Agility. Stamina will give you health points, pretty straight. Strenght will add to your damage and, most important, increase the damage blocked by your shield. Agility is not that important. It helps a little on dodge and criticals, but you need too much Agility to get any real difference.
Defense is a skill, but as a Tank you'll need lotsa defense. As a crude rule (non-confirmed, but works ok) everyone (including mobs) has a skill on weapon/attack, 5 points per level. It means that a level 60 mob has 300 points in attack. As a 60 warrior you'll have (with no talents) 300 defense. It means you're equal to the mob.
Defense skill gives you Dodge and Parry percentages, and if your Defense is higher than the attack skill of the mob the crit chance of the mob is diminished. So, more Defense = +Dodge, +Parry and -Criticals (on you ).
Equip:
Erm... You need gear with a good armor score, and +defense stats, with Stamina. Simple, huh :\
For the end game you'll need about 7k armor and 6k health, and many many + defense.
Talents:
Some people say that Full Prot is not necessary but I think that the Protection tree talents are much needed. Improved Taunt, Defiance, Improved Shield Bash... All those are very very helpfull when tanking and trying to get, generate and mantain aggro from mobs. Some important talents:
(effects on maximum level)
Anticipation: +10 defense skill
Shield Specialization: +5% Block chance and 100% chance of generating a rage point on each block.
Defiance: 15% more threat from attacks when in Defensive Stance (it affects Heroic Strike)
Improved Blood Rage: 50% less health spent on the Bloodrage ability
Last Stand: gives you 30% of your total health for 20 seconds. That's the time necessary for someone heal you or to hold the boss that extra time needed to kill him. Many times I popped Last Stand and then died on the end of the 20 secs, but the boss was killed before I fall
Imp. Shield Block: Get only 1 point on this talent, the 2 other points means nothing and are not worth.
Imp. Sunder: Less rage spent = more sunders
Imp. Shield Bash: 6 seconds silence after a bash. Caster killer. Lots of aggro.
Shield Slam; Good damage, good threat and can dispell one magic effect and can be used disarmed.
Tactics:
Attacks generate threat, +threat = +aggro from the mob on you.
Normally, you'll do the pull. Pulling is an art and you must train it. With time you'll learn about the distance wich each mob aggro, where's the best place to pull what mobs, where to use ranged pulls, etc... I did Undead Strath so many times that I was able to pull 1 mob from a group of 3 in certain parts, just knowing the best place to stay and when to shoot. Charge Pulling is not a great idea most of the time, and without the Tactical Mastery talent you'll lose the rage when changing to Defensive Stance.
When pulling multiple mobs in places like Stratholme (more than 5 mobs each pull) use Demoralizing Shout. Demo shout doesn't generates A LOT of aggro, it generates a little aggro on multiple mobs. The catch is, if you use demo shout on a group of mobs and your group focus on attacking your target, the other mobs will keep attacking you and not them. That's because all mobs start at 0 aggro with everyone, when you use demo shout they all go like +1 with you. If nobody attacks the mobs, they'll be +1 with you all the fight and not mind the others on your party. That's why everybody should be /assisting the main tank when doing complex pulls. The main tank must pay attention and target only one mob and hold until it's down, and try to focus the problematic mobs first (elite, casters, etc...). You must train other types of pulls. Body pulls, ranged pulls, FD pulls, shackle/silence/sheep pulls. In all cases, Demo Shout is good to attract more than one aggro.
After the pulling you must build aggro, and faster. In end game raids it's normally your task command DPS ON or OFF and measure how much aggro you got. The best way to build aggro is with Sunder Armor. Sunder armor stacks to 5 times, so after you've landed 2-3 sunders on the target the DPS can start. After stacking the 5 sunders, there're two chains of thinking: one of them is to use Heroic Strike as the secondary aggro generator, and other is to use the "Shield Block + Revenge" combo. Revenge generates more threat than Heroic Strike, but a critted Heroic Strike generates more aggro than Revenge.
The truth is, it all depends on your rage. When you pull you'll normally pop Bloodrage to get enough Rage to do the initial Sunders. After that, some bosses will hit you so hard that you'll have a full Rage bar all the time of the fight. That way you can just "turn on" Heroic Strike (when you activate the ability it hits on your next swing) and start Shield Block/Revenging. With the Improved Revenge talent your Revenge has a 40% chance of stunning the enemy for 6 seconds, it helps against normal mobs and lesser bosses, but not the high elite ones. Shield Bash is a good ability to maintain aggro, but has a large cooldown. Normally, in non caster mobs, you can land a bash between revenges/Heroic Strikes. With caster mobs try to save it for when it's really needed.
DO NOT TAUNT WHILE MANTAINING AGGRO.
That being yelled, remember: taunt steals aggro for 3-6 seconds, it doesn't GENERATES aggro. If you use taunt on the middle of your aggro maintenance you can be surprised with the mob being aggroed somewhere (rogue crit, spell crit, healing crit on you) and discover that your Taunt is on cooldown. Try to let Taunt ready for when you see the mob running for a caster/healer/stuff so you can get him back. And don't forget to use a high threat ability after the taunt, like a Sunder or Bash, because if you taunt and don't generate aggro the mob will run back to the previous target.
Remember that you can attract the mob using a high threat ability like sunder or shield slam, too, it's just harder than using taunt but it's completely possible.
I think that's it. O'course that there're better guides and better ways to do it, and I can be wrong on a lot of stuff, but well, hope it helps.
EDIT: Information about pulls and Demoralizing Shout