I agree that Disc is great. Shield anyone who might take damage, PoM the tank before he pulls and shield him as soon as PoM bounces off him. Keep him shielded always. Penance for your tank/big heal. Renew/Flash Heal for spot healing, Prayer of Healing for your group heal. Your whole spec is built around Shield and mitigation, so Shield should always be your first line of defense.
You can also use Holy to heal heroics if you prefer more reactive healing. I'd do
something like this with the last two points in Healing Prayers, Test of Faith, or Body and Soul according to your preference. I'd suggest Flash Heal and Dispel glyphs and a third of your choice. Keep three stacks of Serendipity on the tank all the time. PoM rolling always. GHeal is your big heal. Renew is nice for keeping DPS topped off and/or warlocks. Circle of Healing is great and Circle of Healing followed by Prayer of Healing can bring the whole group back from the brink of death. And just because you're Holy doesn't mean you should forget about Shield entirely.
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