How will you do it? Will you go shadow if you are holy? Will you go disc if you are shadow?
Personally, I will heal instances as I level up, so my talent spec will reflect this. I will of course take Spirit Tap :D but then I'll stay on the disc/holy path:
http://www.mmo-champion.com/talent/?priest=05323001303051205000000000023505000032005000000000000300000000000000000000000000
From this, i'll put points as following:
71 - Power Infusion (mostly for instances)
72 - 4/5 Mental Agility
73->77 - 5/5 Rapture
78,79 - 2/2 Grace
80 - 5/5 Mental Agility
I was also considering surge of light, but i don't have the points, as i think grace will be a valuable asset. In case I change my mind:
http://www.mmo-champion.com/talent/?priest=05323001303031205000000000023505000032005200000000000300000000000000000000000000
Then: Mental Strength, PI, Mental Agility, Rapture.
Anyway, the first thing will be to get rid of some of the gear I have (sets for solo/dps and healing). Fortunately, I'm an enchanter. And clear up space by transfering the mounts and pets (I did the quests for worg, spider and other pets) to the new tab. Same with marks, badges etc. And I'll go get a new haircut :P