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I'm just trying to get a rough idea of which spells are first priority and specific uses for some spells.
Renew: Always up on the tank and a convenient way to patch up those who took some splash damage. Also something you might want to keep on Warlocks. Else their life-tapping might let you jump to wrong conclusions :)
PoM: Keep it on cooldown. Let one loose whenever the cooldown is up. Also excellent when you need a quick heal and FH would take too long.
Binding Heal: Use over FH each time YOU took damage. That way you can heal yourself AND the tank at the same time. Much better than having the tank drop while you're busy healing yourself.
Flash Heal: Quick patches of health to those in need. On a well-geared tank, it's usually all you need during heroic trash pulls along with Renew and PoM.
Greater Heal: Your most efficient heal, and truly a nuke. It's the bread & butter of a Holy Priest. Take note of your average amount healed with it. If the tank engages a boss or pack of mobs, start casting GH. Once his health drops by the average amount healed by your GH, allow the cast to go off. Otherwise interrupt the cast and immediately start casting again. For one thing you'll have a chance to gain some extra mana, for another, you effectively fight the rather long casting time of GH by almost always being "halfway there"
Holy Nova: Not to be underestimated, especially when glyphed. If you're standing back with other casters, it's a quick and easy way to heal those around you. It is totally awesome though when you happen to have healer aggro and are waiting for the tank to pull a mob off you. You can heal yourself without making matters worse, because Holy Nova doesn't create threat, and you can do so while running towards the tank.
Circle of Healing: Quick and easy way to deal with AoE damage. Just that.
Guardian Spirit: Best freaking healing spell in the game, because it does exactly what the tooltip says.
There should be more info in the sticky.