For Magmadar you want ya MT and the melee DPS down at Mag, MT at front, all other melee DPS at sides and rear. Pretty much your full priest force keeping MT up with secondary healers keeping Priests, Melee and Hunters alive.If you're lucky you might have 1 healer left over to provide healing for everyone else but most of the time if you're not mentioned above you're fending for yourself.
Everyone else works at max range, behind the MT who's facing is towards the back of Magmadar's cave. If you stay at max range you wont be hit by Mags fear and you'll also avoid his breath weapon. You can't do much about his lava spit, just get out of it fast and suck it up - bandaids ftw in this fight. Spread out as much as possible, to minimise casualties from the lava spits.
Why Hunters you may ask? 1 answer - every so often Magamadar goes into uber psycho mode, he gets bigger and starts to hit much, much harder - if your Hunters don't Tranquilising Shot him at this point its all gonna be grim n brief. Your Hunters will need to set up a chain - along with emotes so that the next hunter knows if the previous one has missed - CTRA can handle the set up of nice big warning messages so no worries there.
This is a long fight, but with the exception of the lava spits its pretty predictable so long as your MT maintains aggro. He's gonna need a shed load of FR gear as this encounter really hurts. Magmadar has around 800K hps so he is going to be a mob like you have never seen in WoW before, you're also on a timer cos if you take too long the Dog packs will respawn and it's game over.
The important thing is not to panic, it sounds daft but a hell of alot is going on in this fight, the key lies with the ranged DPS - as in terms of doing the harm they win or lose this fight, overaggro and you'll wipe your raid faster than anything, lack of awareness with lava spits results in the same, getting too close and getting feared will also get you killed fast. You need steady high DPS without anyone going too mad, with enough people and focus this is a very satisfying encounter to win.
Tips for the lava spits - if your hit by a spit or a spit lands near you, move to a position where you are as close to the spit as you dare, without actually being in it. Magmadar tends to spread his spits around, and unless you are very unlucky, he wont spit near the same location twice for a considerable period of time. If you are hit by a spit its going to hurt - to the tune of 400 damage every 3 seconds or so, even once you leave the fire, make sure you have things like whipper tuber roots, healing potions and health stones available to you. Down them to buy yourself some time, get well back away from the encounter area so you wont get spat on again and sit out the Spit DoT, afterwards you can bandage back up and pretty much keep yourself vertical without a priest or other healer giving you a second glance (which they probably wont be anyway
).