Welcome. Most of your questions are answered in the FAQs and Guides sticky at the top of this page, as well as in the Wiki (see menu at top). Please check those out. You'll find some nice efficient leveling builds there as well.
You'll want to put your first 5 points into Spirit Tap, get yourself a wand, and then stack Spirit (with Intellect and Stamina being the other stats you care about). Later as Spell Damage becomes available, that becomes your primary stat. Use your spells until the target is at about 30%, then wand it to death. Don't forget to use Renew before fights and shield as needed until you get Vampiric Embrace. This makes solo play extremely efficient.
As a priest, you will often be asked/expected to heal in instances whether you're Shadow or not. If you get a piece of healing gear as a drop or a quest reward, it's a good idea to hang onto it, so you can swap it in when you need it. Just how far up a Shadow priest can heal is always a subject of debate, but certainly at least to the Outland, and most agree that with a healing set you can do it all the way to 70. On a similar note, you'll also want to familiarize yourself with the basics of healing and maybe look into a healing add-on such as Healbot, even though you don't intend that to be your primary role.
Giantpooh wrote:
switching from horde to alliance
Watch out for Hogger.
Edited, Jul 10th 2008 1:39pm by teacake