After people were gaining too much exp without even doing everything, they went and toned down the exp gain. This was back during beta. So, as it stands right now, you kind of want to do every little exp rewarding thing possible as soon as you can. That means quests, fights at your level, secrets, waypoints.
At least in the early levels, it's almost mandatory to do every little thing to keep up with the level of the next area you should go to.
