So you've put in the time and effort and grinded (ground?) rep and gear to the point where you have the 372 average iLevel gear. Said gear is all genuine tank, PvE gear (ie it doesn't have intellect, agility, haste or crit on it, it DOES have dodge, parry or Mastery on it, is Strength / Stamina and it's all Plate). You've put (at least) blue quality gems in all the slots and maximised your Combat Table Coverage and Stamina as much as human(oid)ly possible. You visited your friendly neighbourhood Enchanter, Leatherworker and Blacksmith to get all your enhancements, including a trip to Deepholm and Vashj'ir to visit the Therazane and Earthern Ring Quartmasters for the shoulder and Helm enchantments. And you're ready to Look For Raid. What do you need to know about tanking in Dragon Soul on LFR?
Ctrl-i and queue. The Siege of Dragonrest Temple is easier than the Madness of Deathwing, so I would suggest starting there.
First thing you need to do once you zone in is find out who the other tank is. This is pretty important information as you don't want to be wasting taunts on your fellow tank rather than the healers getting pasted. The easiest way to find out is to hit O to bring up the S(o)cial pane, and select the Raid tab. Now look for the little shield logos next to the players. There should be two, one coloured in and one outline. One of these will be next to your name, and the other person is the other tank. Don't worry about the Main / Assist designations as these are random. Once you've established who the other tank is, I like to mark myself and him to make it nice and clear who should have monsters pounding on them for eveyone involved. While everyone is still buffing up, zoning in, take the time to quickly inspect the other tank. If he's sporting a lot of 397 or greater gear, especially tier pieces, it is fairly safe to say that he is an experienced raider. Look especially for 403 weapon / trinket as this will mean that he's killed Deathwing. You can skip this step if you see a "Destroyer's End" title. If he's sporting a range of PvP gear / 346s you're going to be in a bit of trouble and you'll need to step up a bit more.
Anyway, you've got into a LFR group and you've lucked into a tank who seems to know what he's doing, let's get killing stuff. Almost all the trash is in groups of 2 or 3, see what your co-tank pulls and pick up 1 or 2 of what's left. After no time at all, you'll reach Morchok. This is one of the easiest raid bosses in the game to tank. Just go and stand right on top of your co-tank and DPS to your hearts content. If your co-tank get's 3 stacks of Crushed Armor you can taunt off and tank for a bit. When he starts channelling black blood, leg it behind one of the rocks that falls down around the edge and wait till he's done. Rinse and repeat.
Once Morchok is dead, head into the temple itself and hop on one of the dragons. Just follow everyone else. You'll either end up at Warlord Zon'ozz or Yor'sahj the Unsleeping (see below). Warlord Zon'ozz is also known as the Ping Pong boss, but it's a pretty rubbish game of ping pong on LFR mode. For the trash before the boss, pick up the Biggest mob and tank it. It's a massive tentacle. The rest of the raid should burn down the eye first and then the other smaller adds and finally your tentacle. For the boss, your co-tank will likely tank the boss and there is nothing for you to do, so just DPS as best you can. If you are tanking the boss, just tank him where he stands, on normal you have to point him at the raid and then away, but on LFR it doesn't matter much at all. I have heard it said that if the ball doesn't point at the raid it doesn't gain stacks which might mean that you don't do quite as much damage in P2 but I can't confirm or deny this. To play it safe it might be worth pointing the boss towards the raid until he spawns his Orb and then turning him around after it is out.
The next boss is Yor'sahj the Unsleeping (or the blobby boss as my raid calls him). Just kill the trash, you should group up and spread out and kill things in certain orders, but on LFR you either have a strong leader or you just muddle on. This boss is almost a 1 tank fight, so if you have strong co-tank, let him handle most of it. But watch is stacks of Void Bolt. If he gets 3, taunt the boss. Be especially wary of this if you are letting a Yellow slime through as the stacks will rise much quicker. If there is a black slime and you aren't currently tanking, pick up as many adds as possible to take them off you're squishier members.
After Zon'ozz and Yor'sahj are dead you will head up to the top of the temple and from there into the Eye of Eternity. Be wary of mass summons to the EoE, these are likely from jokers pulling you into the WotLK version of the raid. The trash for this boss is actually a bit trickier than most of the stuff we've seen so far. I always whisper my co-tank and say I'll take right, he can take left. Just pick up the group on the right and try and drag it towards the middle to help your healers get range on both of you. I say "try" and drag it, as there are a few casters around who will need silencing with something like Avenger's Shield in order to get them moving. Don't just stand in Blizzards and AoE. The last trash mob will be a big guy on his own, head for the edge ahead of the boss fight. If your co-tank is tanking this fight, there isn't a whole lot for you to do, but you can still be very useful if you keep a close eye on the DBM cooldown for Focused Anger and stand off a bit when it's almost ready, as soon as she starts casting it taunt from outside of melee range and she will immediately stop casting. Your co-tank will likely pull back immediately, just crack on with the DPS. In P2, be very wary of the ice walls (assuming you've just killed a pylon, rather than being electrocuted). She's dead, collect 250 Valor Points and hopefully go Gem and Enchant all the tasty new gear you just got. Coming soon, Madness of Deathwing half of the LFR.