This is likely common sense, and has probably been posted before, but I didn't find it searching so there is only one way to find out!
Anyway, a little leveling technique I've always used for alts to help them on their way through those last levels (usually around 69) is to NOT do their class specific quests until 69 or so.
Class specific quests give large amounts of experience for your level, but they scale in experience to your level. A quest that would have given you 1000xp at 10 will give you better than 10 times that in the 60's. However, the difficulty of the quest doesn't scale. Imagine, plowing through a level 10 quest and getting maximum Outlands exp for it at your level.
By class specific, I mean the various pet quests for Warlocks, water form / cure poison for Druids, and so on...basically any quest that your trainer gives you. Many of these abilities aren't actually needed while leveling. For instance, Warlock pets - I just use my IMP and level Affliction. If I want to do Demo later, the Felguard is talented pet, so no need to train it. Those are really the only 2 pets you need to get to 70. The other pets (and Warlock quests, such as the Orb, etc) can be saved until the experience from those quests will REALLY help, such as during the Outlands levels.
As a Druid, I got over 50kxp doing the level 14 Cure Poison quest chain at 69.
Anyway, like I said, its common sense if you think about it, but based of the number of people I've talked to that didn't think about doing that, I figured I'd throw it out here for others.
Here is my Paladin, at level 52, doing the level 12 Redemption quest:
And here she is turning it in at 52:
As you can see here at Redemption - Quest - World of Warcraft , at level 12 that quest should have only yielded 900xp, but instead I received 7350xp. Note that she is also only 52; had I saved this until 69 I would have gotten many thousand more exp.
Edit - Added Screenshots.