Priest is two classes in one. Solo, you level as Shadow and kill things yourself. In a group, you are the healer everyone is waiting for. You can do both, you just lean one way while leveling.
Leveling spec: Shadow
Go Shadow to level. The key talent is Spirit Tap, which gives you a burst of mana regeneration every time you kill something. That single talent is why Shadow priests rarely stop to drink, and it makes leveling far smoother than healing spec.
- Shadow Word: Pain on the pull, Mind Blast, wand or Mind Flay while it ticks, finish.
- Use Power Word: Shield when a mob reaches you, so you keep casting instead of taking hits.
Use your wand
Buy a decent wand at every level bracket and use it. Wanding costs no mana, so on a soft mob you open with a spell or two and wand it down, saving your mana for the next pull. Priests who ignore their wand drink twice as often.
Healing in groups
You can heal dungeons while levelling Shadow, you just cast more carefully.
- Learn to downrank. A lower rank of Heal often tops a tank fine for a fraction of the mana, and mana is your whole limit.
- Renew on the tank before big pulls, Flash Heal to react, the big Heal only when there is time to cast it.
- Power Word: Shield and Shadow buffs make you wanted in groups even in Shadow spec.
At 60
Priests raid two ways. As Shadow, you bring the Shadow Weaving debuff that boosts the raid’s shadow damage, plus your own damage. As Holy or Discipline, you are main raid healing, with Power Infusion to hand to a caster. Most raids want a couple of Shadow priests and the rest healing. Either way you are valued, which is why priest never struggles to find a group.