I know I've said before that I'm not a Tank. But I really do love tanking. And I do keep up with tanking.
And yeah, if you invite me to tank a PuG on an instance I need, I'll do it with my crap tank gear. Just remember I have crap tank gear. You'll need a very understanding healer and DPS that understands threat. Truth is, many PuGs, after hours spent in LFM will take anyone wearing Plate. There's just not enough tanks available most of the time.
First some tank resources:
This was just on WoW Insider in their Tank column:
If you're LF Tank, read this first. She's 100% right on. Particularly about the folks that play DPS classes. They generally think it's the Tank's job to control aggro. No, it's the Tank's job to Hold aggro. Control is largely in the hands of DPS. I like the saying, "You Pull It, You Tank It." :P YPIYTI ("Yippi Yitti") Of course, no good tank actually does that, but we think it a lot. Specially when we're running around gathering up mobs from over anxious DPS dealers (or worse, the ones that can't aim and hit targets that aren't locked yet!).
All warriors, particular tanks, need to hit this spot regularly:
Everything you ever wanted to know and need to know about tanking, regardless of what flavor you are. They even have T-Shirts! :D
Anyhoo, tanking is a fun way to go. But warriors get pulled in different directions. Do I go DPS? Do I tank? Do I mix it up?
Arms warriors like me need to go one way or the other with their spec. Straight Arms is not going to win you many spots in a 5-man or Raid. So you have to lean Prot or Fury. Arms/Fury is more common, particularly in PvP. An Arms/Prot spec isn't used very often, but if you find yourself tanking a lot, it's worth considering. It's one of my favorites and I used it for ages. Some of the hints about warrior abilities coming in WotLK indicate Arms tanking is about to get a nice boost, as well. :)
Your role, though, is going to be primarily as MA (Main Assist) or OT (Off Tank) for your Tank. You do need to put out enough DPS, but control it so that you don't pull aggro. You should rarely need healing beyond a Renew or Flash Heal for AoE damage when being MA. You should also be able to switch quickly into an OT role if cc resists, or ranged DPS or heals pulls aggro. So macro your Shield and Def Stance dance. Be sure to be able to switch back with a second macro. If your MT knows you'll do this, you'll make their life a lot happier and less complicated. And they'll invite you to run with them again and again!
As the "second piece of plate" you should always have an eye on your MT's healer. Pretty much constantly, regardless of your assigned role. Most very good healers don't like to over heal, so they run it really close. Most of the time they won't pull, but if it gets hot (cc resists, for example, or adds jump in) they can be running pretty close to the aggro threshold. Suddenly they'll get two crits in a row and going leaping and bounding over the MT. Any mob the MT hasn't hit in the last few seconds is going to come off. Or worse, the adds come in from behind or at an angle and the MT can't get them. It's your job to step up and snag 'em.
#1. You do have your threat meter up and running right? Good. You should be keeping an eye on the top two. #1 should be your MT and #2 will normally be your MT's healer or top DPS. Both need watching and if they start getting close or matching the MT, get ready.
#2. Start the fight with Intercept or Charge. Assuming it's not resisted, this will mitigate a little damage off your MT. Charge builds up your rage, but puts you in Battle Stance which will lower your DPS. Intercept has a longer stun, but you have to Blood Rage before you use it. Of course, being in Zerker Stance will get you a heap more damage too, so watch it. Anything you can do to make your MT more mana efficient is a Good Thing. More important, you want Intercept cooled down so you can use it again if the MT's healer gets in trouble.
#3. Pummel is your friend. And your MT's friend. Most DPS warriors completely ignore it unless they've pulled aggro from a caster. No. Use it on any trash mob that's healing and any mob that's casting at your MT. Saving your Tank from having to trinket a Fear is a huge win in most fights. It will be greatly appreciated.
#4. You have three stances, so use them when it's appropriate. You'll get a feel for it eventually. But, for example, if an add comes up and starts casting at you, don't just sit there in Zerker and take it (and die). Switch to Battle or Defensive until cc has a chance to get the mob under control. If your healer has to heal you, make it as easy and mana efficient as possible. It's better to drop your dps temporarily than bleed the healer dry.
#5. Know and use your entire toolset. Offer to refresh Heroic, Demoralizing, and/or Commanding Shout and Thunderclap. Less for your Tank to worry about. Your tank is going to be in a rotation to generate threat not damage. It's a lot of work. Help him out. A mob going after your ranged DPS? Buy the tank a few precious seconds and pop Piercing Howl or Hamstring the sucker. The better you use these side abilities, the better off your group will be. Remind the group, when appropriate, that you have Intimidating Shout and are happy to take a turn scattering adds.
#6. Be ready to OT in a pinch. cc gets resisted. Adds and pats happen. The game is suppose to be unpredictable, otherwise it wouldn't be much of a game. As said above, macro your stance dances and be prepared to put all that expensive armor and that pristine shield to use if the need arises.
If you can prove to be a valuable addition to a group, a lot more people will be willing to include another plate wearer. Let the MT have the MT gear he doesn't have yet, but DO roll for DPS gear. And certainly roll for any MT gear the tank doesn't need. It'll only help you OT better.
The average Arms warrior doesn't get a lot of invites. To get 'em, you have to prove you're worth 'em. It's worth the effort. :)