Do what teacake said.
Look at PoH as a way to get everyone's health back up until you can sneak in a refresh on their shields.
If you are 80, be sure you have hotkeyed Divine Hymn, and don't forget to use it in a pinch. Also Hotkey PoH.
You want your PoH to be as fast and powerful as possible. To that end, I present you with the following macro:
#showtooltip Prayer of Healing
/cast [target=player] Power Infusion
/cast Inner Focus
/cast Prayer of Healing
Because the spells don't share a common cooldown, they all fire with one keypress. Since one spell being on cooldown doesn't stop the other from activating, you can press the key repeatedly to do your multiple PoH.
Why would I want to tie these together?
As disc, if I'm casting PoH, the group is probably taking some significant group wide damage. By utilizing PI, IF, and PoH on the single keypress, I get:
- Reduced casting time on multiple PoH by .5 sec each for 15 seconds.
- Reduced mana cost of multiple PoH by 20% for 15 seconds.
- The first PoH mana free with a crit rate increased by 25% (putting the chance to crit and proc bubbles above 50%).
- Even if PI or IF is on cooldown, PoH still activates normally, meaning this is "keybind it and forget it".
It takes a bit of practice to get the hang of healing AOE damage. You may also simply be a bit weak in the spellpower, or dps could be taking too long on a fight like Loken.
Definately pre-shield your 5 man group before combat, and try to keep shields up on all 5 for the duration of combat. When you can't, and it gets ahead of you, PoH, Binding Heal, Divine Hymn if you have it, all can be useful to get you back to a point of shielding. Keep renew on at least the tank. PoM of course. If you have a lot of mana, you can also keep renews up on other party members along with the shields. They will still be ticking when the shield is used up. This isn't something you will want to do all the time, but it's one option when damage is heavy.
A lot of factors determine your success in AOE healing. Just going Holy isn't necessarily going to keep everyone from dieing. Don't underestimate the importance of your ability to shield. It really is your spec defining talent.