We all have those first 39 levels before we get our epic mount. Before that golden 40th level you have inferior abilities, and you travel painstakingly slow. This is where I come in to help. I have a level 80, and I am in the process of leveling my new warlock to level 80 as well. So here is the lowdown on easy leveling.
First of all when you hit level 20 you gain three very important things; your first mount, new abilities and the ability to enter the BattleGround Arathi Basin. These are all important in different ways. First, obviously new and improved abilities help you kill things faster and stay alive longer, which makes for faster leveling. Of course your mount helps you move around the world of Azeroth faster which helps with questing.

Arathi Basin is a surprisingly good way to level at the early parts of your bracket. For instance, you could go from level 21-24 in about 3 games if you win. This is because the exp rewards at this level are higher than when you get into later levels. The reason I didn’t mention Warsong Gulch is because in Arathi Basin, you get exp whether or not your team “capped the flag”. In Warsong Gulch, there is often what is called ‘turtling’ which is where both sides play defense (normally because they have each other’s flags) and this makes games last forever with hardly any exp. In Warsong Gulch games are often pretty evenly split since you recieve exp throughout the whole game. Also, your team doesn’t “give up” as much.

Also, whenever you do BG remember to pick up the ‘daily’ quest from Orgrimmar. This rewards you with extra honor, gold, and exp. It also boosts your reputation with Orgrimmar. But remember, Arathi Basin should be done sparingly, the best way to level is always through questing (unless you are a mage of course). But the daily quest makes it slightly more rewarding. An added perk of doing BGs is that you come out of them chock full of buffs which you can use for questing. In fact, when I know im going to have a hard fight I go into Warsong Gulch, get some buffs and /afk my way out. Cruel, I know, but the twinks can handle it.

Also I advise getting a questing addon, such as QuestHelper to help with waypoints and other questing notes. Until you ding 80 (or unless you have alot of cash) I would advise getting 2 different gathering skills. For casters Herbalism and Skinning are good choices and for melee classes I would advise mining and skinning. Have fun in the world of Azeroth!