My group doesnt have a dedicated healer, so I use a system I call "fall through" healing. F1-F5 applies to each character respectively. 3 of my characters can heal. On healer 1, if i hit my f1-f5 key it will heal that person. On healer 2, if I hit the button my macro says "Heal character X only if healer 1 is dead". On healer 3, I hit the button and it says "heal the player only if healer 1 and healer 2 are dead." Then I have some modifiers which make everybody heal, which i can use in OH CRAP situations.

Thats how I do it, im sure others will reply with their strategies.

Good luck.