Another link post, to invite you to read interesting blogs about healing and raiding.
First, a fine post by Kestrel on Kestrel's Aerie about sites to visit and read when you're a raiding healer.
He points you towards World of Matticus and Plus Heal, that are very large and good resources for healers. But also to less obvious sites about loot and raid bosses videos.
As a healer, knowing how to heal, how to use your skills, is an obvious first. But then, if you want to raid, any raider arriving on a new boss should know the upgrades he wants, and know the strats. Healers are no exception to this rule :P
And then, a fine post by Kyrilean on Casual Hardcore about DKP. I'm not a big fan of DKP myself, but I can't see a serious raiding guild going without it. I found his post and the description of the DKP system of his guild interesting, perhaps you will too.