Warrior is like any class in the game. Easy to play, but difficult to play well. A good warrior is a rare thing, but in my experience, the tank is the single most important role in turning a good run into a great run.

I have two warriors, a 60 tauren (who I haven't played since BC. :roll:) and a 62 night elf. I won't go into great detail, but here's some general advice.

Talents
For levelling, I have always used fury, simply because it is the best for grinding. Some prefer to level with arms, but fury is widely considered the "best" levelling spec. I recommend respeccing at 70 to something that better suits your endgame plans. (Arms for PvP, Fury for PvE DPS, or Prot for PvE Tanking.)

For levelling, I place my talents like this..
Example Fury build at level 50

Once that is done, I start placing point into Protection. The reason for this is that from 0-50, I don't do a great deal of instance runs. But from 50-60, and especially from 60-70, I do quite a lot. Also tanking is more difficult in 60-70 instances, and talent points in protection are helpful.

Same build at level 64

I finish off the build with more points in Fury.

Same build at 70

Then I respecc. Here are a few example builds to get you started. Mess around with them as you please.

Sample endgame PvE DPS build
Sample endgame PvP build (replace Poleaxe spec with whatever weapon you intend to use.)
Sample endgame PvE Tank build (What my warrior will use at 70.)

Soloing
Bring bandages, that's about all I can say. Playing a warrior is very aggressive. Your plan is always to kill them before they kill you, and that means you must have little or no regard for your own safety if you want to do it well. You can use Intimidating Shout to "stun" a target for a few seconds while you bandage, but other than that, 100% of your time should be spent dealing as much damage as possible.

Keep Battle Shout up at all times, and once you get to level 50, keep rampage up at all times. The increase in dps from that buff is astronomical. (Anyone else remember the bug with rampage on the PTR? )

The build I've recommended is for dual-weilding, so dual-weild with it! Any weapon will do, but ideally, a slow main hand and a quick offhand (ie: a dagger) works well. Try to keep your crit rating high with a fury build.

Instances
Basically, the most important thing to know about tanking is that it is a group effort. You cannot tank well if you have a mage throwing fireballs at one target while a rogue stabs away at another. Use raid target icons to show your group which target they are supposed to be attacking, then generate as much aggro on that target as you can. If your group are not dps'ing the correct target, your job is made twice as difficult, so make sure the others know what to do.

A tank has two jobs. 1, Mitigate damage. (mitigate means "to make less severe.") and 2, hold aggro. (Keep the mobs attacking you!)

Also, this seems obvious, but when tanking, 99% of your time should be spent in defensive stance, and 100% of your time should be spent wielding a shield. Without these two things, you're not a tank, you're just a walking hunk of metal. You might want to step out of defensive stance to charge a pack of mobs rather than using a gun to pull, or to cast Berserker Rage for fear immunity, but 99% of the time, you're in defensive stance.

Step 1 - The Pull.
Hit bloodrage, then pull with a bow or gun. You don't need a high gun/bow skill, it doesn't matter if you miss. You're just getting their attention. Once they get to you, you should have a little rage built up from bloodrage. Use this rage to cast Demoralizing Shout. This generates a little aggro on all the targets around you, and decreases the damage they deal to you. It also does no damage, and therefore will not break cc effects like sap or sheep. If you feel it is safe, you may also use Thunderclap to generate a little more aggro and mitigate a little more damage, but this ability is expensive, and can break cc, so be careful.

Pick up the mob that your group are attacking and start casting Sunder Armor on it. Once you have 3 stacks of sunder, you're relatively safe.

Step 2 - Tab!
Tab-tanking is a great way of holding aggro on small packs of mobs. (2-4 targets) All you do is cast Sunder Armor, hit Tab to target the next mob. Repeat the process until all the mobs around you have one sunder on them, then return to the main target of the group.

Do this, and not only will you have a head start on the dps'ers on the next target, but you're also working to keep aggro off the healer. Be aware that If you are not generating aggro on a mob that is attacking you, it will eventually run off to your healer. This means you need to hold a small amount of aggro on everything.

Step 3 - When things go wrong
Taunt is your friend. But if you don't treat it well, it might decide to bite you! Taunt works like this:

First of all, Taunt bumps you up to the top of a mob's aggro table. Then, it forces that mob to attack you (regardless of where you are on it's aggro table) for a short while. This means that if you are already on the top of a mob's aggro table, taunt will do nothing at all. Save it until you need it.

If a healer gets aggro, taunt the mob, generate a little more aggro on it for the sake of safety (one sunder should do) and then get back to what you were doing before.

Bosses
The techniques outlined above are enough to get you through trash mobs. But bosses are very different. Most DPS'ers in your group will be able to generate far more than your sunder can hold, and some bosses will hit you very hard indeed. Luckily, bosses rarely come in packs, so you'll only have one target to worry about.

Shield Block is one of your most useful abilities. It is practically a guaranteed block of the next attack (next 2 attacks when talented) and even more importantly, it lights up your Revenge ability. Revenge becomes available immediately after an attack is blocked. It deals next to no damage, but generates a LOT of aggro. Here's a list of the abilities you will use most while tanking a boss.

Bloodrage (If your rage bar is getting too low, 0-10)
Demoralizing Shout (aggro and mitigation)
Sunder Armor x5 (Lots of aggro, weakens the target)
Shield Block (mitigates damage)
Revenge (generates aggro)
Heroic Strike (If your rage bar is getting too high, 80-90)

In general, it is best to use as many of these abilities as often as your rage bar will allow.

That's about all I have time to write for now. Hope it's useful.