Below are listed a few Horde-favoring areas and quests you may wish to visit and complete while leveling for the reason of simplicity and swift ascension in levels.
This article is not intended as a leveling guide, a Places to Farm list, or a list of specific zones designated for an eternal grind. Basically, If you ever thought something along the lines of "man, if only I had known beforehand that such a large number of quests were implemented into this zone to be completed simultaneously and with little effort," we encourage you expand this list with your findings.
1 to 10[]
Unless you have a strong dislike for the aesthetic in your starting zone, or have done it several times before with different characters, you're probably better off leveling from 1-10 in your race's territory: (Eversong Woods, Durotar, Tirisfal Glades or Mulgore). Incidentally, tolerating the said zone for your race until at least the level of 4+ is a wise decision, as traveling on single-digit levels throughout adjacent areas tends to throw more difficulties and hinders your voyage to 80. If you desire to change zones, all Horde starter areas are connected to provide easy travel between them while avoiding ?? areas. Forsaken may walk to the Undercity easily; Orcs and trolls may leave the Valley of Trials south through the Hidden Path to Ratchet and then fly to the Undercity (if flight path is acquired); otherwise, a long trek to the zeppelin stations outside the gates of Orgrimmar can provide transportation to Tirisfal Glades or Mulgore; blood elves may travel to Silvermoon; Silvermoon and the Undercity are connected via the Orb of Translocation.
10 to 20[]
If you have 
you may want to level from 10 to 20 in the area called Ghostlands for several reasons:
1. If you pick up the quest chain that starts with 
[1-30] The Farstrider Enclave and ends with [1-30G5] The Traitor's Destruction you will find that the quest reward for the final quest is an excellent blue weapon (
[Staff of the Sun], 
[Farstrider's Longbow], 
[Dawnblade] or 
[Sin'dorei Warblade]).
2. Afterwards, you should be Exalted with Tranquillien and you may purchase 
[Tranquillien Champion's Cloak] for about 25
.
Also, 4 quests are notably close together in the troll area southeast [1-30] Attack on Zeb'Tela , [1-30] Shadowpine Weaponry, [1-30] A Little Dash of Seasoning and [1-30] Bring Me Kel'gash's Head!.
20 to 30[]
Hillsbrad Foothills is the most obvious zone for leveling, but be careful on PvP servers ( Ashenvale and Thousand Needles is an alternative). There is a nice [24] Battle of Hillsbrad quest chain and some other quests available in Tarren Mill. The main two areas you'll find yourself fighting is the Hillsbrad Fields including the Azurelode Mine and the surrounding area for the bears, spiders, and lions; the other zone of focus is Durnholde Keep.
30 to 40[]
You may now wish to venture onto the Shimmering Flats in the Thousand Needles because this area is not only excellent for grinding but for every creature here a quest is also available at the racetrack.
When you picked up all the car parts first you're send to ratchet and booty bay (don't forget to pick up the fp). when in booty bay it is recommended to drop the quest of hemmingway in Stranglethorn Vale (pick up the fp at grom'gol) and continue to Swamp of Sorrows (obviously pick up the fp there too). In swamp of sorrows you can also pick up a quest that will get you send to badlands. Fly back to Grom'gol Base Camp and go to Undercity by zeppelin and make your way down to badlands for the early level 40's. Bring along 1 
[Frost Oil] for 
[37] Coolant Heads Prevail, 1 
[Gyrochronatom] for [37] Gyro... What? and 1 
[Patterned Bronze Bracers] for [42] Stone Is Better than Cloth. you can let friends make these or buy these items from the auction. The quest [37] Gyro... What? will continue with another quest where the reward is 
[Nifty Stopwatch]
40 to 50[]
40 to 45[]
As noted at the end of 30-40 and questing in thousand needles you will have two quests to complete in badlands after visiting swamp of sorrows. Additionally badlands is quitte a nice place for a few levels. after Martek the Exiled you will probably like to continue with [37] Study of the Elements: Rock , [40] Barbecued Buzzard Wings , [40] Coyote Thieves and [39] Badlands Reagent Run , they are all pretty close to eachother and close to inn. Additionally the elementals are a good place for getting 
[Elemental Earth], the coyote and such are really good sources for skinning, also the coyote have a good drop rate for the Darkmoon Faire related 
[Soft Bushy Tail]. the quests named above all share creatures needed to kill (elementals for study and reagent, buzzards for reagents and cooking quest, coyote for reagents and thiefes). additionally this is a good place for herbing and mining but also for grinding.
[Staff of Jordan] is a world drop in badlands, so if you're extremely lucky you might get one of those as well.
Also, be careful to avoid the level 55 buzzard and the patrolling ogre boss that travels with an escort of ogres and you'll be fine.
45 to 50[]
The area Tanaris has many quests for the level range of 45 to 55.
50 to 60[]
The area Silithus is a easy place to level , it's full of quests and easy mobs. But it's a PvP-zone, so if you don't like PvPing you should do Burning Steppes.
60 to 70[]
70 to 80[]