my first was grundrak - found it pretty hard and used to wipe on sladran a lot until I found my pally cleanse button lol, the collosus was a pain and I used to wipe on him time and again, I finally figured out not to worry about the slime pools and just heal through them, arrange your guys in a square pattern around the circle so they always have a clear shot as the ele like to move around a lot. The rhino boss on the other side can be frost shocked out of his transformation so you could have that on a castsequence. The last boss is just dps/heal race, he gets a lot easier when you get slightly better gear, just remember to park your guys in the corner where the tombstone is dps like crazy in troll form, have your tank run in circles out of range when he's spinning and heal like crazy when the rhino appears, he hits like a truck so keep the tanks heals up - he has great tanking gloves.
Ooops, almost forgot eck! - after you've cleared the room arrange your shammies in a square pattern around the entrance to his lair, this is because if your tank doesn't hold aggro he jumps around a lot so when he does all your shammies will still have a clear shot.

UK - prince - keep your shammies on follow and as you get close to him start dropping totems, I ignore the tombs and have a castsequenece macro on my shammies for thunderstorm to take care of the adds. Just heal regularly and take it easy. If things start going pear shaped drop yuor earth eles to take the heat off. You'll also get an achievement for not shooting the tombs . The next two guys need to be taken down at the same time or one of them will spawn a shadow version of himself which is a pain, so just alternate your dps and finish off with a chain lightning, they also have adds which the castsequence thunderstorm can take care off.
The last guy is a pain and I wiped so many times on him I almost hung up my boxing hat, eventually my gear got a bit better and I was able to take him, park your guys clumped together at the end of the bridge with clear access to either side as you need to strafe when his flying axe comes at you, if it connects it's a wipe. Just tank him and heal the tank fairly regularly and chain heal the shammies and it'll be fine.

Draktharon Keep - my favourite instance - still tricky but a lot of fun - first boss tank/spank - that's it. Second boss, run in next to her and put your teams back to the wall facing her, several small waves of ads will come out but they're easy, once the waves are finished she'll attack, dps her and chain heal until she's around 50%, at this point I drop 3 fire eles and as she concentrates on them, heal up and dps like crazy. Third boss is a tank and spank with a twist, put your shammies to the right hand side of the stairs facing the dinosaur park and drop some trmor totems as the king fears. Just dps and keep the tnks health topped up. The final boss is crazy fun, park your shammies at the top of the stairs and have a trmor totem or two out, he's not hard and I got him on the first try (ive wiped since lol) just keep your heals up, he'll change all your team into skellies and change your casting bar so that you only have 4 buttons. I usually just press whichever is up next on the gcd and that seems to work, when you get near the end of the skelly bit, stop pressing the button and just click the 4th button which is a shadow bolt so that your tank has aggro. After the skelly bit I always heal up before dps. It sounds complicated but it's actually pretty easy and he has nice drops. Beware the mobs in the first hall, the little ones should be taken out asap as they cast a shadow pool on the floor beneath your casters which if you don't strafe out of straight away is a wipe.

get the deadly boss mods addon

instances i'm having trouble with are:
halls of lightning, first 2 bosses are easy but the lightning guy just wipes the floor with me, even after watching hachoos video - meh.
violet hold: was there tonight and wiped on trash >.< - I really hate this place, I also hated that other one in CoT where you had to run around too - I really need the tanking pants from here but the repair bills are killing me.
UP: really hard for me - don't know why.
CoS: I really don't like instances where you have to go through a whole story just to get to the action, plus I wipe regularly here too, I should be able to do this .... no idea what I'm doign wrong but I just keep wiping.
I haven't been anywhere else on heroic.