One thing that will help your healers considerably on tantrums is to setup a cooldown rotation. Raid Sac, Hymn, and some other stuff I can't remember exactly. Our healing team had a whole list of people and which tantrum in sequence they would blow a cooldown on. Just put the order in a macro so it is easy to inform everyone what the order is, and make sure each person knows when they are next.
For positioning, make sure there is seperation between the melee and ranged groups. Also you can have the melee all together tight just behind his right or left foot. Then when they run on light spark, they run to behind the other foot, are still in melee range to dps, but are out of light spark damage range. This was really helpful prenerf with meeting the enrage, but isn't strictly essential now.

