If you joined a Preferred world, you get a "Road to 70" buff that doubles your quest experience, and causes you to be a much higher level than your quests. If you do anything other than the main quests with a fireball icon, such as daily roulettes, you may overlevel as well.

Don't worry about overleveling. Your level doesn't matter. Only the level of your main quest with a fireball icon matters, because it gates content and areas above that level.

The other quests you should do are the blue quests because they unlock things, unless they appear at a guild because these ones unlock classes you may not want to play yet and fill your armory chest with gear.