Start simple. Make a macro you can spam the snot out of and not use up all your mana right away. ( I use a /castrandom macro with several ,,,,, to allow me to spam it). Then have another key that you can use for emergency tank healing (i.e. it only heals the tank using your big heal). Then make a macro that throws out a small heal (Flash Heal and or Renew) for each party member, including yourself, and put them somewhere convienent. The number pad was convienent for me, but I also have a g-15 keyboard so I use the left side now. Once you level up it a bit it gets more complex, but easier, for a priest at least. You will have several AoE and incidental healing options.