I go the lazy route and tag

/assist focus
/follow focus
/startattack
/cast [ability]

on nearly all of my abilities.

I run into some trouble when one of my characters is tanking and the other is dpsing large mobs since the follow will often make my second guy run to through the mob entirely and face my main. Ideally I'd just put follow+assist+start attack on one key and spam that as necessary. This route works decent when both are DPSing.