As a healer make sure you take care of your UI. Set up whatever raid frames you are using to clearly show all the information you need such as debuffs, personal defensive abilities, external defensive abilities and absorbs.
Here is my UI in combat:
Mouseover Healing Macros
Unless you are using an addon like Clique I suggest using Mouseover Healing macros such as this:
/cast [@mouseover] Healing Wave
You can do this for all your targeted healing spells.
Cursor Healing Macros
/cast [@cursor] Ancestral Protection Totem