What I did in WoW and Rift for that was basically look at the area in which you're going to fight the boss. Mentally map out a grid over the area and then line everyone up together in one corner. Then, when the AoEs start hitting your alts, just move everyone up one square each time until you hit the edge, then right one square, then start backing up one square each event. Rinse & repeat. Some fights (like the Elemental Colossus in Gundrak/WoW) are such that unless you outgear things, you need to constantly move. For those, I do the same thing but just make sure everyone is lined up together (may require several "runs" back and forth to get everyone lined up properly) and then run forward to engage the boss on one side, then just start backing up pulling the boss along with you. Then when you're all the way at the back, run forward to the front again and start backing up with the boss. It depends a little on distances, what kind of AoE you're talking about and other variables but the basic principle holds for most things.

Smedbox also has some good points about your movement key setups and other configuration options that can dramatically affect the way you do these fights.

Bottom line, though, is that unless you're willing to pay consulting fees for someone to train you, it's just gonna take high-level suggestions to get you started and then lots of trial and error.