In World of Warcraft, Priests are one of the pure healing classes and have experienced a huge surge in PvP representation amongst the top Arena teams when teamed up with a Rogue. This WotlK leveling spec is to take all talents which increase damage, reduce downtime and improve solo questing/killing ability whether it is in the form of utility talents or straight out damage.

Priest Leveling Spec

Due to the fact that some people want the option of healing in instances, they will pick Holy to level from 1-50 while they are doing WOW leveling. However the fastest World of Warcraft leveling spec with the least downtime is Shadow Spec (14/0/57)

Why is this build efficient?

Meditation: Meditation is one of the best mana management talents. This stacks with Spirit Tap to get up to 80% mana regeneration. The amount has been buffed from 30% to 50%.
Spirit Tap: Gaining mana back after every kill, stacks with Meditation.
Shadowform: Pretty much what makes this build, increasing your dmg output and making you less squishy. The 15% more shadow dmg also applies to shadow wands.

Rotation

Vampiric Touch > Vampiric Embrace > Mind Blast > Mind Flay

Gearing Up for Priest Wotlk Leveling

Focus on getting the highest DPS wand for your level as this will be a major way to do damage while you are regening mana. Load up on +spirit gear to reduce downtime as it compliments shadow talents.

Glyphs

Glyph of Mind Flay
Glyph of Shadow
Glyph of Shadow Word: Pain

The other way to increase your level speed is to buy WOW leveling service that helps you get your wanted level in the most efficient way, you get what you pay for.