Your two main aoe spells are PoH and CoH. You should be using CoH often to top people off. PoH is your bigger heal. Use it as often as you need too.
Keep yourself Shielded. Keep PoM active. Keep renew up on the tank. Depending on damage and your mana pool, keep renew up on the group as they are taking damage. Shield someone about to die. Flash heal as you need it. Greater heal if you need it and you have time. Divine Hymn will do wonders for a group in trouble, and Guardian Spirit for the tank if needed.
Other than the tank, it's not so much a rotation as reacting with the best spell when needed.
Disc priests don't have CoH, so they would replace its use with spammed PW:Shields. You may want to consider trying disc and keeping the entire group shielded as much as possible.
If you are a lower level, tanks won't keep agro as well. You should have fade bound to a hotkey you can hit fast when adds come at you.
Edited, Feb 23rd 2010 10:35am by dadanox