Everyone has their own system.

I generally handle heals with my healer assisting my tanking toon and then casting:
/cast [help] Heal Spell; [help, target=targettarget] Heal Spell; [target=party1] Heal Spell

Actively playing the healer could work out well for some as well, as the poster above me attests.
Most posters here seem to play the tanking toon, and macro the heals/dps.
To each their own, everyone finds a system that works for them.