Note: As of 6-25-07, I updated this post to the best of my ability to compliment the changes to the Preist class and WoW gameplay that came with the expansion.
Hello, my name is Covello (
http://img413.imageshack.us/img413/7717/nakedpriest15fn.jpg).
While leveling my Priest to 60, I tried out multiple specs and strategies, and found the best possible way to grind to 60 in regards to both speed of kills, amount of downtime, and exp/h in general. After experimenting a little, I gave my friend a spec to help him level his Troll Priest to 60. After 35 levels, it's going extremely well; he loves it. He had played a Shaman and 2 Mages to 60 and aided leveling a Warlock and Druid to 60, yet still you'll hear from him, "I @@!!ing love Spirit Tap". I tried grinding myself, and it works extremely well. We have zero downtime and are able to easily break 20k/h as low as level 35.
The Gear
You will be Wanding a lot... a lot. It's important to wand to allow your mana to regen. Stock up on Spirit gear. Buy some stuff at the AH for cheap. Get massive Spirit gear! It'll make grinding so easy. Collect all Cloth gear from SFK. Run SM like a bot in your 40s. Don't waste money on Staff of Jordan; you can get Zum'Rah's Hexing Cane (
http://www.thottbot.com/index.cgi?i=38853) a few levels later by running ZF a few times and it's a better staff.
Always get the highest possible DPS wand for your level.
Look up "cloth armor 20-40" at the AH. There are tons of great Spirit items that'll help you a ton if you're willing to spend a few 10g's.
There isn't much +spirit gear that has +damage on it, and Spirit is your primary stat. Avoid 'Shadoweave' gear in your 40s... the +damage isn't worth the Spirit loss. Darkness and Shadowform offer all the +Damage you need.
Remember, Spirit > Damage > Intellect = Stamina, just don't gimp your life
too much, especially on a PvP server.
The Talents
10-14: 5/5 Spirit Tap
15-19: 5/5 Wand Spec (I'm serious.)
20-21: 2/2 Imp SW:P
22-24: 3/5 Shadow Focus
25: Mind Flay (This skill SUCKS before lvl36 anyway)
26-27: 5/5 Shadow Focus (HIGHLY recommended over Blackout)
28-29: 2/2 Imp Psychic Scream (Filler)
30-31: 2/2 Shadow Reach
32-34: 3/5 Shadow Weaving (Best available, not a grinding talent)
35-37: 3/3 Focused Mind
38: VE
39: Silence
40: Respec to
http://www.worldofwarcraft.com/info/classes/priest/talents.html?000000000000000000000000000000000000000000500252010051103051000
41-45: 5/5 Wand Spec
46-47: 5/5 Shadow Weaving
48-49: Whatever you find yourself needing. If you chose to use VE and want more healing, Improve it. If you use Mind Blast a lot, get Shadow Power. That's probably what I would do, it'll help more as you progress in levels.
50: At this point, I would do another respec. Yeah, respecs may cost a bit of money, but it's what helps grinding, and you'll make the 6g back in Outlands in about 2 minutes.
http://www.worldofwarcraft.com/info/classes/priest/talents.html?000000000000000000000000000000000000000000500252010251103051251
51-55: Unbreakable Will or Wand Spec, depending on what you want. They both kind of suck equally at the period you're at. I guess Wand Spec would be better overall for grinding.
56-57: 2/2 Martyrdom, this and Imp PW:S will be nice for Mind Flays.
58-60: 3/3 Imp PW:S
61-63: 3/3 Meditation! Congratulations on 60, you now have a third excellent mana talent to further aid you. Try and fit this talent into any build you make, except I suppose Arena Shadow.
64: Inner Focus
65-67: 5/5 Shadow Power
68-70: Whatever you find yourself needing.
MUCH Later Added (6-26-07):
VT is a great talent, and by this point, you'll find yourself wanding less and less. Also, once you reach Outlands and start amassing +dmg gear, you probably wont need to wand at all anymore. You should be able to simply Mind Flay down your target, along with your two DoTs of course, without any need to stop. As your damage gear increases, which it will greatly in Outlands, the time you save making fast kills will easily outweigh the time you spend drinking, especially with Spirit Tap and VT to help.
I haven't played a Priest in a very, very long time, he's still sittin there at 60. Either way, this guide should still be accurate. I edited a bit with the talents. It's hard for me to say past 60 as I haven't tried it yet, but it's obvious that Shadow is at favor for grinding speed.
The Pulls
Wanding will be a MAJOR part of your grinding. Be sure you have the highest possible DPS wand for your level. I always Wanded at 40%. This gave me time to passively regen mana and then when Spirit Tap procced, I was already outside the FSR and regaining to 100%.
Just pull with Mind Blast, immediately SWP while strafing away (don't back up, it's slower... the mob should just be hitting Mind Flay range as the global cooldown ends), then Mind Flay three times, it should reach you midway through the 3rd Mind Flay. Begin wanding. You shouldn't ever need to use VE or Renew. If you do, the mobs are probably too strong. Move to a lower area.
Green-level mobs are your friends. They're ideal for Shadow grinding. If your life is still getting too low, don't shift out, just Bandage and/or Cannibalize. That reminds me, LEVEL FIRST AID. Anyone without First Aid is an idiot. Anyone without First Aid IS AN IDIOT!
If you have ANY downtime whatsoever, you either were PvPing in between pulls or you're doing something wrong. There's not much damage gear available at your level, and the 'Shadoweave' gear sucks because of the lack of Spirit.
If you respec to Discipline, pull with Holy Fire, then Smite, then Mind Blast. SWP should be after one of those 3 spells, depending on how fast the mobs you're grinding die. Some that die really fast I don't dot at all (Power Infusion up, anyone?). Some that last a while I dot right after Holy Fire, and occasionally I will dot after Mind Blast.
Leveling a Priest completely SUCKS before 40... then after that it's a blast. I loved 45-60.
Good luck.
SIDE NOTE: The peak of a Shadow Priest's PvPing is in his 40s. Hands down the best times I had on my Priest was fighting off 2 gankers with a mob in my face in Lost Rigger Cove, or learning how to beat Druids and Paladins way back in STV. In the high 40s, a Priest has all the Shadow talents he needs to be effective.
All the other classes that rely on their 21/30 or 31/20 specs won’t have the complete build they need to be effective. More importantly, no one is decked out in T2 gear with an axe in your face. Everyone has equal gear, and you don't need to switch to a raiding spec to get gear to keep up and gimp your PvP. If you're on a PvP server, Enjoy the 40s. Take it slow. You won’t regret it.
Also much later added (6-25-07):
For a priest at 70, it's much different than what it used to be. Shadow is now a viable and acceptable group spec. Holy is not a steaming pile of crap anymore, and actually has a little survivability. Discipline is still my favorite spec, great in terms of mana and fun without Shadow damage.
Depending on what you intend to do at 70, you may need to spec a little differently. Those of you who would like to raid most likely will need to start off as a healing spec. I strongly advise that anyone with a 70 Priest gets their rep with Tempest Keep and Cenarion Expedition up to Revered, and runs Heroic Mech and Heroic Slave Pens, as well as any other heroics you can get into, on a regular basis. Getting the money, gear, and Badges from these instances is the fastest thing you can do to gear up.
It would be miles easier to find a group with a healing spec rather than a shadow spec, though.
Keep in mind, if you intend to be Shadow long term, you're going to need the gear to be accepted for it. The first place to start with this, aside from getting Badges, is to level Tailoring. It isn't cheap, but the Frozen Shadoweave Set (
http://www.thottbot.com/?set=553) is some great gear for the effort you put into getting it.
If you want healing gear, you can also level Tailoring, only instead of Shadoweave tailoring, go Mooncloth tailoring. Great healing gear there, too.
If it's just money you're after, try Enchanting or Jewelcrafting. Though both are very, very difficult to level, and they offer the biggest rewards once you get the big recipies needed, although the recipies may also be difficult to come by.