I keep my team at the entrance of the room where the first 2 mobs are that you kill before the boss. My team just strafes out of the "fire" when they need to.

For the lever phase, i make sure i am at full health then throw a PW:S and renew on. I use Word of Glory to keep healed up if i need on my tank. I also used some speed potions/ boot enchants/ and/or the talents from the ret tree that give run speed increase while i was learning the mechanics to pull the levers faster. After i get back up to my team at the entrance to the room, I AoE the rest of the snakes down then interrupt the boss with only my tank. Then I run back to my team for the rest of the fight.

With a Disc priest i would suggest getting shields up on all your team at the beginning of the phase to reduce the damage they take. I just spam a few prayer of healing and that usually keeps my guys up. I am running a holy priest so i don't know it that may help any or not. I also used some speed potions/ boot enchants/ and the talents from the ret tree that give run speed increase while i was learning the mechanics to pull the levers faster.