The way that I first had it setup and probably the simplest way is like this.

Create a macro similar to this:
#show heal spell
suppressmacrofailures (this stops the annoying macro failure pop up messages)
targetexact Tanks_Name
cast heal spell with long cooldown
cast heal spell with shorter cooldown
cast instant cool down
targetlasttarget (so once you have cast the heal you target the enemy again and can get to damaging)

Put that macro on a spot 8 on your main hotbar ( this is just an example)

In ISBoxer create a new keymap in the Combat keymaps. The step in the keymap wants to look like 8->cleric_character_name.
Then bind that keymap to a convenient key. Now whenever you hit that key on your keyboard the cleric will heal the tank using the macro.

That is a nice simple way of getting heals working. Initially I used that and had macros bound to the extra keys on my G15 keyboard to heal any of my 3 characters. I still have it setup for emergencies.