I recommend Zygor's Leveling Guide. The guide is in a small window on your main screen in-game. All the detail that you need to complete the quest is included. You’ll never have to switch back to a website, or even the in-game main map to see where you have to go or what’s next. The guide is available for both Horde and Alliance.
I use Zygor's guide for leveling and I highly recommend it.