The Care and Feeding of Warriors is as always here for you, the reader, oh and also because Matthew Rossi is some kind of demented idiot who will do something like get out of tanking a raid and then spend two hours grinding on some Blade's Edge quests on his draenei warrior before logging onto his tauren for some PvP.
The first caveat is that warriors tend to be the twitchiest tanking class, especially as you first learn the class. It can often feel like you have to mash buttons constantly in order to hold onto your aggro lead, and even then adds will often peel away from you when they'd stay right in place for a bear or paladin tank. It takes time to really learn and get comfortable with the somewhat frenetic style of the class, and to a degree this translates out into soloing or questing, depending on what spec you're using. I'd suggest checking out Tankspot and browsing the forums, although the theorycrafting can get pretty thick over there.
If you are tanking a mob that does a lot of casting, consider working Spell Reflection into your rotation, once you have it of course. Don't just pop it every time you have enough rage, but try and keep enough rage (and the ability needs to cost less rage, in my opinion, it's too expensive at present) so that you can use it when you see a mob casting. Against casters like Darkweave Syth, not only can the ability protect you from a great deal of damage but it can also provide you with significant aggro based on the damage they do to themselves.
The easiest way a warrior has to tank multiple mobs is called tab-targeting. Basically, you gather the mobs you'll be tanking up around yourself as best you can, and then use your sunder or devastate on each of them in turn, hitting the tab key to change targets until you've gotten them all. This can be made easier with macros that make it so you don't have to change targets at all - one macro is called the 'mouseover sunder' because it applies a sunder effect to a mob without you having to deselect your target or even do any damage at all to it, meaning that you can sunder CC'd mobs without breaking them out of CC. For ease of use I'll reproduce the macro here.
There is also a combined devastate/sunder macro on the same page just below the mouse over sunder macro. With or without the macro, tab sunder/devastate is a very inefficient way to tank multiple mobs, but it is basically the only way you have as a warrior. You can throw thunderclaps into the fray as well if you're in a safe place to do so (ie, won't break CC) and use Demo Shout, but neither really generates so much threat that you'll hold anything in place with them. In general, if you get a lucky shield block during this (because you probably won't have rage to use your shield block ability and will have to rely on your passive block) you may be able to throw a revenge at a mob, or perhaps a shield slam if you get lucky on rage generation, but don't expect to be able to hold more than three mobs without significant help from your party. If they can't or won't give it to you, then you'll fail to hold aggro. It's that simple.
You very rarely can start a pull with more than 10 rage (sometimes you'll be able to let Bloodrage tick fully before pulling, but often you have to hit the button and run in on a boss or start pulling) so you won't be able to just let fly with abilities. When tanking single target (a boss, basically, or when you have enough CC) if you can pop Shield Block just as you reach it you can follow up with a Revenge, giving you a nice dose of threat off of the bat. This is assuming you don't have a triggerhappy party that will give you five to ten seconds to establish solid aggro. If you do, you'll want to take the initial hit from the mob to generate some rage and use either Sunder Armor or Devastate (a 41 point prot talent) immediately. Both are spammable, and if you're in a group that won't wait for you to get into an aggro groove, you'll want to do just that. Either way, once you have five sunders up on a single target, you'll want to switch to a refresh basis and depend more on Shield Block and Revenge for aggro. If you are specced protection and have Shield Slam, use it whenever you can. Do not, however, make the mistake a lot of starting warriors do and use Shield Bash as a poor man's slam unless you are absolutely sure you will not be needing a spell interrupt anytime soon. After using a Shield Slam and a Shield Block/Revenge, consider using Thunder Clap and Demoralizing Shout to help reduce incoming damage which will help make your healer's life easier, but if you do make sure you're not thunderclapping on the CC. Move the mob if you have to, as long as you don't saunter out of healer range too fast. Finally, if you're swimming in rage even after refreshing the sunders on your target, popping Shield Slams, keeping your Shield Block/Revenge combos up, and have your target's attack speed and attack power reduced with TC and Demo Shout, queue a Heroic Strike to use up some of that spare rage you have. I don't like to over-rely on HS myself, it eats rage too effectively to make much use of it in the beginning of a fight, but once you have solid aggro and your rage bar is staying full no matter what you can do then it's a nice move to toss into the mix for added threat.
This is fairly simple advice on tanking rotations, and as you learn the class you'll come up with your own variations and uses of specials. That's fine and to be expected. These basics are not meant to be help up as the perfect standard; they're just a means to start getting comfortable with the variety of options available to you as you start tanking.
Rotations for grinding, questing and non-tanking warriors in groups/raids are a different story, and depend greatly on what spec the warrior is. There's no real 'rotation' in PvP because you use whatever ability you have the rage for depending on the unpredictable and chaotic nature of what the other players you're trying to kill are getting up to - sometimes you'll hit hamstring, or piercing howl, sometimes it's unloading your biggest damage instant (be it MS or Bloodthirst), sometimes trying to fear bomb folks away, there's no standard to what a PvP warrior spends his rage on, and no question of aggro to be maintained. Since I plan on covering warrior DPS specs in more detail soon, I'll leave their rotations for later, as this column is already ponderously long and you're probably all falling asleep. Up next week, warrior DPS specs and rotations!