Basically, just either use standard blizzard frames or configure your xperl/pitbull or what have you to show the debuff. Then, drag him into the fire, then drag him back out, first go try for about 3-4 stacks, then watch his debuff, when its getting close to running out, kite him where he just clips the fire, and try to build up his stacks one at a time, don't let them fall off unless your healer is having trouble keeping everyone up. Most healers don't have a problem til about 10-12 stacks, however, you have to be VERY careful to only get 1 maybe 2 stacks at a time, 2 should be fine til about 6 or 7 after that one at a time, if you fuck up, you will wipe your group, if you don't think you can do it precisely, then let it fall off about 7 or 8. If your dps is good you should have him dead around 10 or 11 stacks. Basically just do it one stack at a time past about 7 and let it fall off when your healer starts to struggle a bit, keep a close watch on his mana and the health of the rest of the group. Although, if your dps is struggling you might want to let it drop off sooner, because heavy aoe heals are stressful on the healers mana supply, so you don't want to risk ooming him if you have to let the stacks drop off at like 12 and he is only like half dead.