I would say the easiest way is to use a macro to quickly target 3 enemies at once. This will handle most enemy groups you come across. First make it so you are targeting enemies only and use the following macro:

/mk attack1 <t>
/nt
/mk attack2 <t>
/nt
/mk attack3 <t>
/target attack1

This should set it up so you quickly tag 3 enemies. Once the mob is reduced, it shouldn't be a problem for dps to handle the 1 or 2 mobs left. All that remains is that you find the priority target and initiate the macro to mark it as 1. The rest should take care of itself.

If you are in a fc or playing with a friend who uses a pc, you can also ask them to mark enemies for you. Most should understand the problems inherent with the ps3, but the above macro is a good standby for those parties where you have to mark yourself.