I tried to come up with many source of horde leveling guide for you all.

This one i highly recommended from wow-pro.com. Very detailed one. This guide got lot of positive comments from the readers. Which quest for you to pick and also have map included to guide your journey. This guide start from level 21, assumed before that you need to to your quest to level up.

Jame's Horde Leveling Guide - Chapter I (21-31)
Jame's Horde Leveling Guide - Chapter II (31-40)
Jame's Horde Leveling Guide - Chapter III (40-51)
Jame's Horde Leveling Guide - Chapter IV (51-60)

Chapter I (21-30) - Journey from the Barrens to the Thousand Needles

Introduction

This guide starts at level 21. However I strongly recommend you follow Hosho's Barrens leveling guide as soon as you hit level 13. That's one level higher than what Hosho recommends in his guide, but I recommend you start it at level 13, it will be easier to do the difficult parts of his guide, and you should be level 21 at the end of his guide then, which is the level I want you to reach before you start with my guide. It is your task to reach level 13 on your own and it shouldn't be a problem, the main reason why I don't want to start a guide at level 1 is because:

1. It's not really needed
2. Depending on your race/class choice you will start from different areas so covering them all would be a mess.

This guide is optimized for FAST leveling with a minimum of grinding sessions. Quests are important, they give rewards and faction and are less boring than pure grinding, BUT sometimes some quests are really a time waste and we will be skipping those and replacing them by good grinding spots when it is necessary. Some people say that grinding is always faster than questing, this is true in theory when you don't know which quests to take and which to avoid, and what is the best order to do them. With this guide, questing will be very efficient and much better than pure grinding. Follow each instruction carefully and you will see for yourself. The quest choices and order to do them are optimal so that you run as few as possible while doing the most possible and then turning several quests at the same time. This guide will be very useful for both veteran and novice players. I try to keep the amount of information as short as possible. So even the guide itself is optimized for the minimum reading possible, to save time! Let's get started immediately then! Everything described in this guide can be done solo (besides when I say otherwise). You can of course follow this guide while duoing, grouping, it's not a problem, it works too.