No matter in which faction you belong, the quickest way to reach maximum level is the same: completing quest after quest toward level 80. This feature is what you want in your horde leveling guide; it should also complemented by detailed instructions so you never waste a second thinking where to go next.

Each race has its own starter zone, so you will have different quests at first and a few of class specific quests later; but after you reach Ogrimmar, the same quests series apply for all Horde character. Let's say you start as a Blood Elf; these are the quests that you need to take in order:

1. Reclaiming Sunstrider Isle from Magistrix Erona.

2. Unfortunate Measures from Magistrix Erona.

3. Well Watcher Solanian from Well Watcher Solanian at the Sunspire on Sunstrider Isle.

4. Solanian's Belongings from Well Watcher at the Sunspire on Sunstrider Isle.

5. The Shrine of Dath'Remar from Well Watcher Solanian in Sunstrider Isle.

6. A Fistful of Slivers from Arcanist Ithanas on Sunstrider Isle.

7. Thirst Unending from Arcanist Helion at Eversong Woods.

8. Report to Lanthan Perilon from Magistrix Erona.

9. Aggression from Lanthan Perilon on Sunstrider Isle.

10. Felendren the Banished from Lanthan Perilon on Sunstrider Isle.

11. Bring Tainted Arcane Sliver to Arcanist Helion at the gazebo of the Sunspire on Sunstrider Isle.

12. Aiding the Outrunners from Outrunner Alarion near the bridge leading south of Sunstrider Isle.

13. Slain by the Wretched from Outrunner Alarion.

14. Completing the Delivery from Outrunner Alarion.

15. Major Malfunction from Magister Jaronis at Falconwing Square.

16. Unstable Mana Crystals from Aeldon Sunbrand at Falconwing Square.

17. Wanted: Thaelis the Hungerer from wanted poster.

18. Delivery to the North Sanctum from Magister Jaronis at Falconwing Square.

19. Malfunction at the West Sanctum from Ley-Keeper Velania at the West Sanctum in Eversong Woods.

20. Arcane Instability from Ley-Keeper Velania.

21. Darnassian Intrusions from Aeldon Sunbrand at Falconwing Square in Eversong Woods.

22. Bring Incriminating Documents to Aeldon Sunbrand.

23. The Dwarven Spy from Aeldon Sunbrand.

24. Fairbreeze Village from Aeldon Sunbrand.

25. Roadside Ambush from Apprentice Ralen.

Doing those 25 quests should get you to level eight already. To be more efficient, it is really important to know where you have to go and what to get first, thus whenever possible you can accomplish more than one quest at once or at least picking a few necessary items in one go.

At level 12, you can travel to the other zones (eg: Barrens, Ghostlands, Silverpine) and do the quests there or continue the quests at your own zone. Whatever your choice, you can follow the quests series there and eventually reach Ogrimmar with no grinding and have your gears updated. Once you get there, you can follow the same horde leveling guide regardless your race. These are the quests in order:

1. Ziz Fizziks from Sputtervalve at Ratchet.

2. Goblin Invaders from Seereth Stonebreak on the border of Stonetalon and the Barrens.

3. Arachnophobia from Wanted Poster: Besseleth.

4. Boulderslide Ravine from Mor'rogal at Sun Rock Retreat.

5. Further Instructions from Ziz Fizziks at Sputtervalve

6. Naga at the Zoram Strand from Marukai along the Zoram Strand.

7. Allegiance to the Horde from Thrall at Ogrimmar.

8. Journey to Hillsbrad Foothills from Apothecary Renferrel at Undercity.

9. Beren's Peril from Allister in Sepulcher.

10. Time To Strike from Deathstalker Lesh at Undercity.

11. Elixir of Suffering from Apothecary Lydon at Undercity.

12. Elixir of Pain from Apothecary Lydon.

13. Battle of Hillsbrad from High Executor Darthalia in Tarren Mill.

14. The Rescue from Krusk in Tarren Mill.

15. WANTED: Syndicate Personnel from wanted poster in front of the curch in Tarren Mill.

16. Dangerous! from High Executor Darthalia in Tarren Mill.

17. Souvenirs of Death from Deathguard Samsa of Tarren Mill.

Completing those quests will bring you to level 24. Again, efficiency is the key here; you'll want to finish as many tasks as possible within the shortest time frame and continue the process until you hit level 80.