Outside MT: Position Halion so the center of his hitbox is about 1/2 way between the wall and the center of the room. The portal to get into phase 2 always spawns relative to where Halion is, so keeping it dead center leaves people more open to breaths and cleaves when they zone into phase 2. Your back should be to the firewall but this will also block your camera. When the meteor falls, the big add will be MDed to you, they are not tauntable so if you are main tanking you really should be (god I swore I would never say this I hate this glyph) using glyph of maul to keep agro on it as they get burned down once the AOE ends.
Add tank: SWIPESWIPESWIPESWIPESWIPE. Sometimes a pet can actually pull agro on it (felguard cleave being the biggest culprit) or the MT can get proxy agro and they will not come to the raid. Just target them while spamming swipe and taunt. Otherwise just keep Halion targeted while mauling and swiping to get that extra maul damage on the boss.
Inside MT: you can either go cat to help dps but I recommend staying in bear and helping pick up the little adds. This will be especially helpful if the add tank gets the debuff and has to run out to be dispelled.
Outside MT: Stay outside and jump around doing nothing. This will allow you to not only get him properly positioned for phase 3 but also everyone will get a threat wipe while you will keep your threat from phase 1.
Add tank: go cat and DPS
Inside MT: Make sure you are the first person inside, he will not activate until hit (or after a few seconds if he is not hit) so feral charge him and turn him to your left. This is to make sure the raid does not get breathed on or cleaved, and specifically left because of the rotation of the orbs. Do not run to fast and run into the back of the beam to your left, this is not pleasant.
Outside MT and Add Tank: same as phase 1
Inside MT: Same as phase 2
Outside MT and Inside MT: The breath is probably one of the weakest breathes of any dragon, use armor neck cape rings organ and sindragosa's flawless fang.
Add Tank: The adds are all fire damage so SFF and either Satrina's/Jugs vit or CSK. Double ring of binding if you have them or ring of binding + devium's or twin valk. I use the Princes's cape (royal crimson) with an FR enchant and I have a spare pair of bracers that I put an FR fur lining on. You can also get the FR helm enchant from Kirin Tor rep if you are so inclined.