Picking the right Horde leveling zones is very important in World of Warcraft. Since you will be going a lot on foot in your first levels, having the right terrain will make a big difference. I will share with you the best zones to level your Horde character from level 1 to 60.
This is important to know for another reason also. Flying mounts will only be made available to you from level 60. Until then you will have to use grounded mounts. You can imagine how much time you will waste when you have to go around hills all the time or have to look for a way up a mountain to do a quest. So here are the Horde leveling zones you should go in.
Durotar 1-10
Northern Barrens 10-20
Ashenvale 20-25
Stonetalon Mtns 25-30
Desolace 30-35
Feralas sau Dustwallow Marsh 35-40
Thousand Needles - 40-45 (This is a really nice area. The content is amazing and entertaining and you will also get your own boat that will go really fast).
Felwood 45-50
For the 50 to 55 Horde leveling zones you have two valid option. Un'Goro which is a jungle filled with dinosaurs and such, or Winterspring which is a cold climate map with lots of Yeti. You can chose either here, depending on what Gathering skills you have.
Silithus 55-60
These leveling zones are chosen by the best players because they balance good content and good terrain very well. And that's what you need in order to level fast in World of Warcraft.
Since you need to do quests only, you need a good environment to do so. Grinding is no longer necessary, at all, since you also get a lot more experience when in these areas. You will also gain more experience if you log out in inns every time. On top of that, there are bonuses to the experience you gain from Heirloom items. But in order to get these items you need a main character to get either Justice points or Honor points with.
Another very good source of bonus experience, which stacks with those two, is the perk you get from being in a guild. If the guild is high enough level, you will get a 10% bonus to all experience gained, even from Gathering. On top of that, you also get a mount speed bonus from the guild, that helps you complete quests faster, since you will be moving faster. So I guess that is a bonus to experience gained too.
When you combine all those bonuses with those great Horde leveling zones, you will level up extremely fast. In fact, you will only have to kill a few monsters at the lower levels to gain a new one. You won't even have to finish half the quests in any area to earn enough experience to move to the next.