This fight is divided into two phases, and given the correct group makeup is a very simple fight. This fight requires three Warlocks and three Priests as well as Hunters' Viper Stings. All of them need to drain mana from Moam. If there is not sufficient mana drain, Moam will do a massive AOE which throws everyone into the air causing first Arcane damage, then fall damage. The AOE can be avoided by running away as well, but is obviously not the method of choice, so just keep him mana drained. Druids and either Shamans or Paladins are the main healers for this fight. Sometime shortly after 50% he will call in three Mana Elementals which do a lot of Arcane damage AOEs. This is at 1 minute 30 seconds. The Warlocks will keep these banished for the remainder of the fight. After Moan summons the elementals, he does not attack for a period of time and his mana drain is slowed. He is usually killed before this time expires. (He is still mana draining the group though, so keep mana draining him to avoid the AOE bomb.) If you don't kill him fast enough, another group of Elementals will spawn, at this point, a wipe is very likely.
When Moam dies, heal up the raid, then kill the Elementals one by one as they do not despawn on his death.