Parte the Firste: Talketh to People...th.
Okay, so the fake old time speech thing? It doesn't work. We won't do that anymore. But frankly, instances are not meant to be dour, grim, silent stormtrooper marches of annihilation. They're supposed to be fun, wacky, bad joke telling stormtrooper marches of annihilation! It's fine to pull fast, especially if the group significantly outgears the place (we'll be talking more about this below) but I've found that in many cases simply typing the occasional line in /p between pulls can actually get four random strangers to talk back to you!
Admittedly, I sounded a bit like a comedian trying to warm up a room before a TV show (I think I said "I like you guys but man you don't talk much") but if you're willing to risk getting aggro from Wink Martindale (see, there's one of those bad jokes now) it can liven the place up significantly. Last night's Halls of Stone run (ugh, not Halls of Stone again) was made significantly easier for me once the group started chattering back and forth at each other between trash pulls because (here's the functional dirty little secret of why this is good for us tanks) it keeps them from running ahead of you.
That's right, there's a reason ol' Matt is telling you to get the group chattering. Chattering = typing. Typing = busy for a couple of seconds, which means they're not running ahead, aggroing packs and then running back to die and get the healer killed because the healer tried to save them and now has mad healer aggro so there's like thirty little stone guys hitting him or her in the face. A group that is talking can still do these kinds of things, it's true, but it's an additional impediment to it, and once you get the ball rolling you often don't have to do more than type the occasional "Wow, that's true" or "lol" and they'll keep it up.
Encourage it. Foster it. Get them to start telling outlandish stories, brag about how awesome they are, trash your server, whatever it takes to distract them so that they stop trying to pull instead of you. Be affable. Get the group to work with you instead of against you. It's hard enough to tank four caster mobs and a teleporting ghost, after all.
Part Two: Make Adjustments
There's a lot of things that you will want to change about how you normally do things to mesh with four strangers. Your guild is used to you by now. They know you're weird about clearing trash and hate to skip it, or that you always do LoS pulls to try and get everyone into Swipe range, or that you never open with Consecrate. They've had time to watch you in action, they know what they can and can't get away with. Likewise, you know about that one mage who always picks the wrong target to nuke into oblivion and have him focused for taunt purposes, or that one healer who is always slightly slow to start healing on big pulls out of fear of group aggro. You've learned their quirks.
Forget all that now. You have no idea who these four people are. You don't know what they're going to do. Stop tanking the same way you always have and start tanking reactive to what they do. If you see the DPS DK is opening with Death and Decay, get ready to bust out a tab targeting storm of cleaves and hit TC/Shockwave every time they're up. If this new rogue burns tricks on you every cooldown... thank him? I don't know what to do when rogues are nice, it throws me. Don't freak out, don't yell at the group for doing stuff you've never seen before, try and react. (This doesn't mean that if they do stupid things like Misdirect onto the healer you can't yell. But vote kicking them is easier on your sanity in the long run, and trust me, if DPS is MD'ing onto the healer it's usually not that hard to get them vote kicked. Save yourself the stress of freaking out.)
Likewise, and this one was very, very hard for me to accept, but here's the thing: I know you ran TotC/TotGC until your eyes wept, or did a boatload of heroics, and you're very proud of your 40k or even more health tank set with gobs of dodge and parry. And I'm happy for you, really. It's very nice. Now take half of it off and stack threat stats.
It's perfectly acceptable to walk into a heroic with as low as 32k unbuffed health if you have to in order to keep threat in the first place. Dump a stam trinket for one with gobs of hit or expertise. Slap on some block value gear, or even a DPS belt and bracers, whatever it takes to hold threat. No one cares how hard you are to kill if nothing is trying to kill you. I personally drop to 38k in heroics in order to wear a Grim Toll, Bloodbath Belt, and several high block value pieces.
I'll be honest, the only reason I choose block value over, say, crit is because I feel naked going below 540 defense even when I know I can be uncrittable in a five man heroic at 536. As long as you're not crittable, dump as many avoidance or mitigation pieces as you have to in order to hold threat. I find instances to be much more fun if I can actually generate some rage and do some damage while I'm tanking, and it makes them a lot faster when people aren't taking dirt naps every pull.
Let's face it: the DPS is not going to wait for you to build aggro. They don't care that you have to ramp up your threat generation (if you do). There's a general mindset among DPS players that their job is to do as much DPS as possible as fast as possible, and while you can occasionally find one who will remember the old days of 'Wait for Sunders, guys" those days are generally gone. This isn't a raid, where if you don't gear for maximum stamina and avoidance the boss will hit you back to back for 35k apiece and you'll die. Trust me: wear some DPS gear if you outgear the content. You'll be glad you did.
Part Three: Remember why you're there
Unless you actually queue'd up because you really like yelling at strangers and dropping group in a snit, take a deep breath. If the group is intolerable and you have to leave it, that's fine, but try and do so in as nice a way as possible. "I'm sorry, but I don't feel like we're really making any headway on this" is preferable to "You guys all suck at getting out of Wells of Corruption and this is the sixth time we've killed all the trash only to wipe at 1% because everyone but me is dead, go jam twigs up your buttocks and dance on a dirty floor".
The second one might make you feel better in the short term, but it fosters a bad mindset. Don't take it that seriously. Put on a really good song and sing off key during pulls. Talk to your dog ("Did you see daddy save that group with Challenging Shout? Did you? Who's a good tank? I am!") or just take some deep breaths, gut it out, and get your emblems. Save your rage for the mobs. Unless you're a paladin or DK, in which case, it's less directly applicable and more a metaphor for using your emotions to motivate you to tank better. But warriors and druids, you go ahead and actually save your rage for the mobs.
Also, I recommend (especially if you have good DPS gear) queuing as DPS a few times, whether on your tanking character or on an alt. Get a feel for how they play. It can help soothe you to just bash away at the enemy without trying to keep them all focused on you all the time, and also can help you understand how DPS can often feel constrained by tanking. It's worth walking in the other guy's shoes.
Now go forth and do whatever you were going to do anyway. I'm not here to run your life.