Leveling a Priest can be quite hard. There's always three talent trees: Discipline, Holy, and Shadow. Which one is the most beneficial for leveling? What is considered the best spec to get you towards the level cap fastest and easiest?
In addition to the best tree and spec, what about areas, quests, and dungeons? Sure, there's some addons offered that will actually let you know the shortest distance and order of quests dependant on what you have on your quest log, but those addons do not show you what quests are great and which of them are the most useful. They only display the shortest way to finish what you've selected. That is hardly efficient.
Dugi's Ultimate WoW Guide is just what you need. It's an addon that has not only the most effective talent tree and spec for leveling your Priest, but it also contains guides for leveling from level one all the way up to the level cap. This guide includes a GPS arrow which will present to you the direction to go, the order of the quests, and tell you exactly what to do so you do not even have to waste time reading the quest if you do not want to.