World of Warcraft is designed for efficient leveling. Experience gained is maximized by moving through zones, completing all the quests for your level, then moving on to the next area. This sometimes means coming back to a zone to finish quests that were above your level initially. For those who look ahead and want to get their flying mount as quickly as possible, and use it the most, the best method is to do every quest in every zone, along with as many instances as possible. It's quite possible to have your flying mount by the time you leave Hellfire Peninsula (even before Patch 3.2), use it all the way through Outland, then have only a couple of zones in Northrend before you can once again use your flying mount.

Use this as a progression guide, matching it to the zones and doing all quests indicated for that zone at each phase, coming back to a zone to pick up those quests which were too high level for you when you were there previously. Group your quests so that you do all that you can in each area of a zone, taking advantage of different quests which rerquire you to kill the same/some of the same, creatures/NPCs.

Zones in blue text are found in Eastern Kingdoms. It's recommended that Blood Elves do all quests in Eversong Woods, then continue on to Ghostlands. Once Ghostlands is completed, move to Kalimdor. Your choice is to start in Durotar and do all quests (for rep), or to start at CampTaurajo. At some point everyone should consider doing the quests in all starting areas, for reputation. Rep rewards give discounts and extra mounts (for achievements).