Move onto the last zone and complete all, or nearly all of the quests available in that zone. By this time, your WOW power leveling helps you get about level 17-18. Go back to the first zone, and complete the rest of the quests there. In my opinion this is the best way to level your character. Generally you want a team of 3-4 people and you must have a HEALER. I recommend a Tank, Healer, 2 damage dealers. The idea is to go and find mobs 10-15 levels higher than your characters and start killing them. You would be surprised how fast you can kill them as the damage dealers kill them pretty fast for the power leveling. If you die in a party with no healer just respawn back to town and leave party. Then you can register in party matching and you will be reinvited back to party and teleport there. Make sure you have plenty of summoning stones!

 

Complete the easiest quests in the first area that you go to (Night Elves should visit Darkshore first, Dwarves/Gnomes should visit Loch Modan first, Humans should visit Westfall first.) Move onto the next zone, and do the same, but this time you can complete more of the zone. Leave the most difficult, unless you can get a group for them - don't waste too much time on it, though. You can also have 3 damage dealers and 1 healer and take turns pulling mobs in and then rooting them. Early in the game you can easily get 2-3 levels an hour this way but as you gain a higher level you will start to slow down a bit obviously.

 

37 is where you obtain your next batch of quests from Stranglethorn Vale. Arathi Highlands has fairly decent quests to get a higher WOW power leveling in Faldir's Cove, or if you're feeling group-friendly, knock out the ones in Stromgarde. Badlands has a lot of nice quests, but you have to actually find them. This is where supplementing experience by grinding becomes more efficient at times, and at 42-43 you should be closing the last of your Stranglethorn quests, and be finished with Badlands and Arathi both, as well. Typically, my "first zone" is Westfall, in which case you can go back when you are done with both Loch Modan and Darkshore, and finish the Van Cleef line of quests and be at a good WOW power leveling to run the instance.