Many of the top players in World of Warcraft are continually seeking new ways in which they can level their "alts" quickly and easily. There are two key components to leveling any class in WoW both quickly and efficiently.
Firstly the talent build of the class is going to play a vital role in the characters skill set and role throughout the game. Each class has 3 talent trees they can acquire new abilities and skills from, only one talent tree can be used used primarily with the possibility of slight hybrid mixes of the 3 talent trees once the first tree has had enough talent points assigned to it.
The build you opt for really will play a key role in your characters ability to level up fast. Some classes are just easier to level than others anyway, but the correct talent build for a class will certainly be the biggest benefit.
You'll also want to tailor your build to the type of role you plan on fulfilling throughout the entire game! Admittedly this is next to impossible if you're just starting out with your first character, but if you've already leveled a couple of different classes then you should be able to pre-determine the type of build that is best suited for you.
For example if you plan on doing lots of solo questing with a combo of mob grinding and leveling that way then you would have a completely different build to that of a character who wants to follow the dungeon leveling strategy.
Dungeon leveling is my next tip for leveling your "alts" of generally your characters at warp speed. This technique is often overlooked as many like to go it alone throughout the land of Azeroth, at least until later levels anyway. Dungeons do require teamwork and unfortunately cannot be conquered alone.
There are many advantages to dungeon leveling though, including more rewarding items in terms of both loot dropped and XP gained. Getting familiar with dungeons and incorporating this into your leveling strategy is a sure fire way to boost the speed at which you level.
Many would suggest solely completing dungeons to level up quickly, however this can soon get boring and I would suggest a mix up of both solo questing and dungeons. Make sure you're always in the queue for a dungeon and on the move in between earning extra XP.
Dungeons are easier than ever now to locate and find groups willing to participate to conquer the dungeon and share the rewards. A player must reach level 15 before this feature becomes active, but once any player reaches level 15 the Dungeon finder tool will appear in the menu bar where you can join dungeon quests.
All in all, you're going to want to pre-determine your leveling strategy between solo questing, dungeon leveling or a combination of the two and then assess the best suitable talent leveling build for that strategy. A good class leveling guide will help determine the best suitable build and different build types whether it be damage dealers, tanks or healers.
One final tip if you're solo questing to level quickly is to know your quest and map out the best routes. If you see a quest giver then always accept the request even if you already have lots in the queue. Then complete the ones closest to each other, cross referencing from your map.
You'll be surprised at how how much time staying organized and planning your journeys saves!