Disclaimer:
This is the way I tank. It works for me. Some of these things are standard and can't be change other things are my preference.
Must Know Tanking Terms
TPS- Threat Per Second. The amount of threat generated per second. This is the number that dictates the max amount
of dps that can be produces on a target. The higher you TPS the higher the ceiling for DPS.
GCD - Global Cooldown. The minimum cooldown for all skills. For all classes other then rogues its 1.5 seconds. For
rogues its 1.0.
DPS - Damage Per Second. This is the thing you won't be doing much of raids... In reality, your dps is the bar that
determines if a DPSer needs to be replaced...if you multiple your dps by 2 :p
CC - Crowd Control. This are abilities that cause mobs to lose control and stop doing dps. Lowers a mobs damage to 0
or at the least significantly lowers the dps a mobile deals.
Protection Rotation
Single target threat Rotation
This is end all be all to max threat; There is NO other way to generate more threat. As a note when talking about threat rotation, you do not see shield block here since shield block is off the global cooldown (GCD).
Shield Slam, Revenge, Devastate, Devastate
-Heroic Strike at 40+ Rage.
Multi-target Rotation (melee mobs)
This is a situation that only really effectively done for 2-4 targets, however its not impossible to tank more. But, don't make the mistake of confusing Multi-target tanking with AOE tanking. It is pretty much impossible to AOE tank unless you consider Challenging Shout to be a effective way to AOE tank.
Start with Thunder Clap (TC) to get initial agro maybe a Demoralizing Shout to mitigate some extra damage
Shield Slam, Revenge, TC, Devistate
-Cleave at 45+ Rage.
Note: If you don't have imp TC you maybe want to throw out a rotation and tab devistate. Use TC and Demoralizing Shout just to put up the debuff.
Multi-target Rotation (melee & casters)
First Option
If you can LOS tank them the same way as if you are tanking all melee. Shield Reflection helps get some extra agro and mitigation, but isn't a big issue if you don't keep it up since TC and devistate will hold agro on them.
Second Option
This is for if there isn't a good place to LOS or you just think your leet or something. This way I usually just throw out Heroic Strike and use either a single target or multi-target rotation and keep enough rage to have Shield Reflection up every time it is off cooldown.
Note: For the 2nd option, if you have been tanking for any amount of time you have notice that the mob you shoot starts moving for a second or two before the rest of the group aggros. You want to get all casters that you have to aggro to start casting at the same time during the pull. So make sure you have enough rage at the start of the fight and pull by shooting a melee or by face pulling to make sure the casters start casting at the same time.
The first shield reflect determines if you or the healer is going to be tanking.
Resources
http://www.wowwiki.com/Threat
http://forums.worldofwarcraft.com/thread.html?topicId=75381044&sid=1