Here is the Priest leveling talents that i have found to be the best to level, however some of the players may want you to heal the group so just have some healing gear ready just incase.

5 Wand specilization
2 Improved Power word: Fortitude
3 Improved Power word: Shield
2 Healing Focus
5 Blackout
3 Shadow Affliction
2 Improved Shadow word: Pain
5 Shadow focus
5 Improved Mind Blast
1 Mind Flay
2 Shadow Reach
1 Vampiric Embrace
2 Improved Vampiric Embrace
3 Focused Mind
5 Darkness
1 Shadow Form
5 Shadow Power
5 Misery
1 Vampiric Touch

ok here is the priest talant spec for leveling again this is more of a dps spec priest but with some elements to help keep u alive while insatncing

http://www.worldofwarcraft.com/info/classes/priest/talents.html?tal=500320113010000000000000000000000000000000000000000000320323051223012325102301351

if you want to be healer (what sure is handy because you can do almost and instance/raid) you need to spec in holy. so thats haves his good things also