You're at the very same point I was at this stage in Wrath. :-) More power to you.

The advice above is good stuff; let me add one thing. Never having healed before, there's a certain amount that's just not going to come across in text. A friend, who encouraged me to try healing, said to me at one point "you can't heal like a DPS" but I had no frame of reference for what he meant.

The Cataclysm stated philosophy of choosing between cheap/fast/big healing spells may actually make it a bit easier to pick this up from book knowledge than it was before, but the biggie for me was this: even though I felt thoroughly underprepared, I learned a hell of a lot by just doing -- and *even though it didn't feel like I was learning in the moment!*

So read the above guides for sure, but don't think you need to memorise them. Copy a spec, learn the main five or so spells, and find a friendly well-geared tank to go with you in your first couple of instances.

And this is a great journey you're about to begin, it's a completely new and satisfying perspective on the game. Have awesome fun.