Post by Hashshashins
1-40 is generally personal preference as far as spec is concerned though I went shadow all the way, got to 73ish and got dual spec shadow/discipline and just quested/healed dungeons to 80, was really efficient. You'll have no real mana issues, especially after 50. Use the stickies here, they're amazing, full of information. Insofar as race is concerned, roll whatever you want, you'll be the one looking at their backside for a long time. Heres a basic list of racial traits though (if you're into that sort of thing, using that to pick which race you choose).
AllianceHuman:
Every Man For Himself Nice for escaping roots etc.
Diplomacy Not majorly important but nice if you know you'll have to grind large amounts of rep at some point (ICC rings for example).
The Human Spirit Once again, not massive but spirit is more spellpower for both shadow and holy through talents.
Dwarf:
Stoneform Not massively useful, it can come in handy in certain situations.
Night Elf:
Quickness Being missed is always nice.
Shadowmeld If you get into a bad situation it's useful to drop aggro though this is limited to soloing in PvE really, in heroics and raids it's very situational.
Wisp Spirit Makes corpse runs more bearable.
Draenei:
Gift of the Naaru An extra HoT, always useful, scales too.
Heroic Precision Arguably the best racial in the game, massively useful even if you plan on healing.
HordeBlood Elf:
Arcane Torrent Useful imo though some people may disagree since mana issues aren't common.
Troll:
Beast Slaying Possibly useful for levelling, not sure how it would do for raiding though.
Berserking Amazing racial, especially for shadow spec at 80, like a mini heroism on a standard cooldown.
Da Voodoo Shuffle Once again, useful, won't have a huge impact while raiding though it will help, most useful during levelling.
Regeneration Not that useful really, it's a weak heal, VE should heal more than it (not 100% sure, my own priest isn't a troll).
Undead (Forsaken):
Cannibalize Most useful for classes without healing spells, this is still a decent racial for levelling, free healing is never a bad thing especially since there will be humanoids to kill for most of your levelling career.
Underwater Breathing Not that useful really, best used to hide in AB!
Will of the Forsaken The reason for so much QQ (the living before the nerf, the undead afterwards). Similar to pvp trinket, this is handy for levelling (for obvious reasons) and for raiding/heroics. Ony anyone?
After that, just read the various things posted by regulars here (OscarDivine, Panik, Paolo), they're always haunting this place. Also check out
Paolo's Blog, tis very good for when you hit 80, some nice insights (and no I wasn't paid to advertise it, hint hint paolo!)