Hi, my name is Ratgirl. I'm a huge jerk. I'm going through forum withdrawal because I promised myself I'd spend some time away from realm forums. I should be studying, but I'm not. I really, really want to see you guys get the third Kael'thas kill on Alliance-side.
I trust that your excellent benevolent officers are going to tell you guys exactly what's going to happen and what to do right, so, I'll tell you guys what's going to go wrong and what to do about it.

Thaladred (the one you kite) will kill people in Phase 1.
Don't be that person who makes everyone groan because they die in Phase 1. No one likes that guy. Note that, if someone does die, he'll randomly target someone else and begin walking toward them without an official announcement--be aware of who he's targeting!
Dying is best avoided by not being near him ever and by being aware of your surroundings.

Capernian (the mage-type one) will be difficult to tank.
Sometimes, she can be an absolute bitch to move around. DPS needs to hold aggro until the tank on her is comfortable--give him or her time! EVERYONE needs to be spread out--Conflag on multiple targets is very bad.
Hint: For this fight, spreading out is pretty much never a bad thing.

Telonicus (the hunter one) will use Remote Toy on an important person.
He randomly casts this on a raid member every 15-20 seconds, and it might hit someone who's tanking a P2 weapon. If this happens, it may be best to wait the 60-second duration until it wears off--there's no rush in P1. Leave this to the discretion of the raid leader.

Not everything will be dead before the next phase.
Sometimes, a weapon or two will be left alive when Phase 3 starts or an adviser will be left up when Phase 4 starts. Usually, when this happens, someone will flip out and say something to the effect of "OH NOEZ NOT EVERYTHING IS DEAD WE HAVE FAILED WIPE IT WIPE IT". Fear not! This will often happen on beginning attempts, and it is absolutely fine. Just make sure that the important people move to the correct spots (i.e. for P4, someone with the staff must be with the MT on Kael) and finish off what you have left.
Protip: Remember, have a shadow priest try to keep Rank 1 SW:P on everything
for Misery and possibly have warlocks CoS targets. It helps!

The weapons will be difficult to loot.
The first time you go for the weapon to loot it, you'll note that, due to crappy corpse detection and the possibility of dead weapons being on top of one another, it'll be really hard to loot. It's fine, just pan your camera weirdly or move or do whatever.

Someone will forget to loot a weapon.
This usually manifests itself on the 11th or 12th try of the night, when the MT says "Oh, fuck, I forget the shield." This can be avoided by someone who isn't extremely busy (a healer) grabbing a couple extra weapons in case someone forgets one. Remember, everyone can loot one of every weapon.

The staff buff won't be up.
Casters, make a macro for whatever spell you use the most.
/use Staff of Disintegration
/cast TheSpellYouUsetheMost(Rank x)

Pyroblasts will kill the tank in Phase 4.
Nightmare Seeds and Greater Fire Protection Potions are your friend. Keep all HoTs on the tank, make sure there is ALWAYS a Power Word: Shield up before the first Pyro, so on and so forth. Make sure you use the shield buff as well, but that should be obvious.

People start dying in Phase 5.
Phase 5 is the easy part of the fight. Really. However, for Gravity Lapse...

• DO NOT TOUCH THE GROUND. EVER.
• Spread out. Remember, you have to spread out on the z-axis too this time. If you don't know what the z-axis is, look above and below you. That's the z-axis.
• When Gravity Lapse is about to end, get closer to the ground. You'll take fall damage if you're too high up.
• Continue DPSing; for some reason, some people think that all DPS needs to

  stop.

Someone gets Conflagged in Phase 3.
Getting Conflagged in Phase 1 is bad and shouldn't be done; you can be at max range to avoid that, as someone will surely say. However, in Phase 3, things are much more hectic and there's a lot of motion. Stay the fuck away from Capernian if you aren't tanking her; treat her like she's Jasmynn IRL.

In Phase 4, there isn't enough DPS on a Phoenix Egg.
Let's talk phoenixes. They'll spawn right around Kael'thas and aggro on someone. They have some terrible aura that does fuckloads of damage; it is your responsibility to not be near them. In <Oblivion>, we had a Hunter kite them around because they were pretty slow with everyone responding to the Hunter's route; I'm not sure what y'all will do.

Anywho, if you don't burn the egg in time (it's not that hard), another Phoenix will spawn. At this point, because Kael is also spawning phoenixes, the raid will become overwhelmed. Consider having a hunter just kite all of the phoenixes in the back of the room to try to buy time, as the goal in Phase 4 is to get Kael to 50% as quickly as possible (as you saw, when Phase 5 is beginning, there's a cinematic and the raid can try to pick off one phoenix at a time in that half-minute or so).

Don't get discouraged.
Many claim that Kael'thas is the most difficult fight in the game to learn, and there's likely truth to that. However, I assure you that this is the kind of fight that feels like you're hitting a brick wall for a while, and then--eureka--you have the attempt. You all know what the attempt is, I don't need to tell you. It's so rewarding to kill him; just be patient, be attentive, and be aware of your surroundings. A bunch of other things will probably go wrong as well, but that's the best I've got for now.

Feel free to PST me in game if there's ANY advice or tips that I can possibly offer; once again, I deeply apologize for intruding your forums.

Kill this jerk, please.