My personal heal macro on my shammy is this:

#showtooltip
/target party1
/target focus
/cast [target=targettarget,help,nodead,exists] Healing Wave; [target=target,help,nodead,exists] Healing Wave


The /target party1 is there in case, for some reason, my focus is lost or I'm using /focus for some other ability. It defaults to assisting the party leader if I have no focus.

Basically this casts healing wave on my focus's target only if the target is friendly. Otherwise, if no friendly target is selected, it heals my main.

My follow macro automatically sets my main as the focus. When party members die, I can hit a "focus personName" button which resets my focus to a new toon for a quick new "main".