Taurens's Beginning
If you're a tauren, you're probably starting at Mulgore, the old and chubby place, full of cows and moos, the first things you're going to do is simply follow the chain quest you get at the beginning up to at least level 10 around in Mulgore, once you do that. Head over to Thunderbluff, you should have automatically learned flight paths you could use and just instantly fly over to the barrens.
Orc's Beginning
As an Orc, of course you do the simplest of quests, slay that, and etc...
Of course you'll skip everything in durotar except the beginning quests
When you hit level 10 you'll start moving to the beginning of the barrens,
Do not go to the Crossroads until you hit at least 13 or 12.
Troll's Beginning
Same as Orc's Beginning
Blood Elf's Beginning
Chain quests and etc etc, till you get to silvermoon, you should have a portal in the top area of the map thers a building, there should be a portal in there
It's a light ball, it should port you to Undercity.
Once you're out of Undercity, go to the ship towers.
There should be a portal to Orgrimmar.
Undead's Beginning
May be requiring a little bit of grinding at the beginning but it works,
as far as I've heard the quests for starter are a little bugged,
if its fine then I'm glad for you, if they aren't you'll have to grind mobs
till level 5 or so and go to one of the towns nearby and again over to the
ship towers and Orgrimmar Portal
More will be added later on as for beginnings....
Note#1: In MoP there are NPCs known as the Kokron, they will kill you in seconds, or less. So take notes! (Crossroads)
Note#2: If you have quests who are like 0/1 slain and etc... and make sure you remember this, you'll find this helpful at the future. So if you got quests who are asking you for like a 0/1, and the mob ain't there, just wait a little, or wait for a person to come, wait a little, see if he spawns. Do not give up instantly.

Crossroads (Levels 10+)
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At level 10+ locate a nearby flight path and fly over to the Crossroads, also note in MoP there are NPCs known as the Kokron, they will kill you in seconds, or less. So take notes!. If you're stuck in the middle of the quests in the Barrens, try heading over to Azshara, there should be enough quests there to be level 20, once that happens.

Ashenvale 20-25
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Go over to Ashenvale, check around the cities for working quests, they might be a little crowded so it might seem like some quests are not working so get ready for a crap storm. Make sure you get up to level 25 at least. Also, Check Note#2.

Stonetalon Mountains 25-30
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Once that happens(Level 25 being reached), fly over to Stonetalon with your freely given flight paths, start over from top to bottom cities, that way when you hit 35 in Stonetalon you'll already be on your way to the Southern Barrens.

Southern Barrens 30-40
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Southern Barrens, is where you should level up to at least level 40.

Dustwallow Marsh 40-45
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You should go Dustwallow, simple and easy quests, and all of em' work, and I know that because I've got the achievement of all completing 48 quests there. Sadly you have no flight paths for this, so you should be riding / walking over there manually. So at Dustwallow you're gonna stay till 45.

Tanaris 45-50
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After 45 was hit fly over to Tanaris and then start questing there, I wouldn't bother with the Arena quest, waste of time waiting for the mobs specially with all the crowd and etc, so just skip, stay at tanaris till 50.

Un'goro Crater 50-55
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At 50 you'll fly over to Un'goro Crater till 55, there's really not much to tell, every town in there works and there's plenty of easy quests.

Winterspring 55-62
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To winterspring you'll go right after you hit 55. Plenty of simple and understandable quests, you should stay there up to at least level 62 to avoid Hellfire.

Zangarmarsh 62-65 / 66
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At Zangarmarsh you'll stay till 66 or 65, it is your choice completely.

Nagrand 65/66 - 68
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Once you do that(Reach level 65-66) depart off the area and start flying to Nagrand, it is your next spot to level. Make sure you do the arena quests because some of them are auto complete and giving a lot of exp. You're gonna stay Nagrand till 68.

Borean Tundra (+ Dragonblight + Zul'drak) 68-76
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When that happens(When you reach level 68), Go to Shattrath and use the Orgrimmar portal, you'll wait for the Borean Tundra ship aka Northrend, the left side to the flight master there's a tower, that's the one you'll wanna be in while waiting for the ship. Borean Tundra should be enough for up to level 76 (If you manage to only get to up to level 72 or 74, try going to Dragonblight first towns and then Zul'drak middle side and quest there, easy kill and return stuff).

Sholazar Basin 76-78
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When you reach level 76, you should fly over to Sholazar basin and you should stay there up to at least level 78.

Icecrown (+Storm Peaks) 78-82
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Once you get to level 78 you'll want to fly Argent Tournament, you can get 4 of the same quest so it'll be super easy and quick, each quest gives 1 mil quest, you should level there till level 80, so as far I've heard Hyjal ain't doing so good so I would recommend leveling at Storms Peaks till level 81/82 (THE MORE THE BETTER), I cannot give a proper explaination for this but you'll want to do that for safety.

Mount Hyjal (+ Uldum. Alternative - Deepholm)
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When that happens make sure you take the quest from Valley of Strength in Orgrimmar, there's a giant Board giving quests. One quest will tell you to go to Moonglade, the portal doesn't work so make sure you learn to fly till then and fly there, complete the quest, then you'll have a quest to head over to Hyjal, the tree, make sure you take ALL quests in the area and try doing as much of the chain quests, you should have enough till 84 or 83, if It's only 83 and a half then you'll want to go to Uldum, it may seem like the quests are bugged but you're still gonna take the Board quest again from Valley of Strength, the map will not tell you where to go for the quests, but you'll need to go to the old and known as a dungeon city called Tol'vir, make sure you go deep inside because it won't be shown instantly, it should be an area with cages and NPCs giving quests, do them and each should give a full bar of XP, you can also quest at Deepholm till 84.

Twilight Highlands 84-85
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At level 84 you'll go and level at Twilight Highlands, you will skip the beginning quest from Orgrimmar since It's bugged, you'll just use the portal and start the quest chains.

Pandaria (And etc+..) Levels 85-90
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When you're 85 of course you want to go to Pandaria, the portal is located in Valley of Honor (Orgrimmar) The areas you'll quest in are.
Jade Forest
Kun-Lai Summit
Townlong Steppes
Dread Wastes

-Credits to Blazemourne
Jade forest Singegruff OR Rivett Clutchpop(372 lvl 85)
Kun Lai The metal paw(393 lvl 87)
Townlong Steppes Alin the Finder(393 lvl87)
Townlong steppes Supplier Xin (408 lvl 88)

Reputation's you'll get along the way:

This could work for alliance if you know what you're doing.
If you have a 90 Character, you may farm a rare spawn dropping this item.
Easy as hell to level with this thing around.

If you'd like to contact me ingame: