
On those missions where the party is not taxing my skills, I find it hard to target say a hoard of Bone Minions (the one that is about to die) or all those npc guards that monsters are slaughtering.
Maybe have a secondary windows of all "friendly" that you can heal show up in a list. Due to the sheer number you could have, make it show lowest health at the top but once you "select" your selection stays on the target you want, or if there at full health, make them not show on the list of allies around you.