[NEW EDIT!]Also works with PALADIN tanks![/NEW EDIT!]
In fact, its easier with a pally. Simply because you can Power Word: Shield them and not worry about rage problems, which leads to loss of agro that then leads to a wipe.
Just something i found while leveling a priest... What did i find? the EASY way through the crap levels, that's what.
How does it work? Holy Nova. That's how.
Simple to do really, get to level 20, get holy nova. Then take your warrior/druid friend to instances (Making sure they are tank spec would help).
Its really simple. Bubble the tank, put a renew on him. He then pulls as much as he can handle, Refresh the renew and the bubble, then proceed to holy nova the hell out of the mobs.
By the end, mobs should be dead, tank still up, Your out of mana, but everything is dead.
Glyph of holy nova is very handy, so get it.
I might also add that as the priest, Go discipline spec.
Hope this short post was helpful as there aren't a whole lot of priest power level guides out there.
