I like to use this format for my heals.

#show
<Insert Assist Method>
/cast [help] Renew; [help, target=targettarget] Renew; [target=player] Renew

You can vary that according to your form of assist.

#show
<Insert Assist Method>
/cast [help, target=focustarget] Flash Heal; [help, target=focustargettarget] Flash Heal; [target=player] Flash Heal

#show
<Insert Assist Method>
/cast [help, target=targettarget] Regrowth; [help, target=targettargettarget] Regrowth; [target=player] Regrowth




Theoretically, you're either targeting your master toon (target=targettarget) or are assisting them.

The first condition will then target the master's target, and if they're friendly it will heal them. So your master toon can target any of the slaves, themself or another friendly for an easy heal.

The second condition comes into play if the first fails. That is, if the target of your master is hostile, then it attempts to target the hostile's target instead. This will almost always be your tank, but could be whoever took aggro foolishly.

If both of these conditions fail, then target=player directs the heal to the caster of the heal spell. You could change this to target=focus or target=Tank's Name.