If you already have a high-level character and want to quickly level up a new one, by far the best tools for the job are the items labeled “heirloom gear.” These pieces of gear have two very special properties — they bind to your account, so any character you own can use them, and they grant bonus experience. Their stats also scale with your character’s level up to a certain point, so you can equip a fresh character with heirloom gear and power through much of the game.
The Horde 12-25 (Barrens + Stonetalon Mountains) guide has been rewritten and revamped.  In addition, there has been numerous tweaks to the speedrun route to make things faster and easier to follow.  Also, in case you haven't noticed I am now adding about 40% more info per step and redoing all the images.  Unlike with my previous vanilla guides, I am now giving a brief explanation of where to go and what to do with each step along with any other helpful tips.
Résumé des informations (TL;DR) : Spoil Terminez toutes les quêtes disponibles, récupérez un maximum de Puissance d'Azerite, faites le Front de Guerre une fois niveau 120 pour récupérer un loot 370 ilvl et accéder aux quêtes, faites le Front de Guerre chaque semaine pour la réputation et l'AP, faites les World Quests pour la Rep/AP/Émisaires, trouvez de l'équipement grâce aux donjons et assurez vous de faire les 9 disponibles en difficulté mythique.

The problem with using your gold to pay other players to do WoW’s busy work is that you have to get the gold to pay them, and the way you get gold is mostly busy work. Many WoW players just want to buy their gold from other players with cash — preferably, amounts of cash that are fairly trivial relative to the perceived value of the time and effort required to obtain the gold legitimately.
Something to keep in mind as well is that this will make enchanting materials more valuable, since it is likely most players will now simply scrap their boe greens instead of getting them disenchanted. Also redundant dungeon/raid gear can be scrapped rather than traded to the (guild) enchanter in the run. Less stuff gets disenchanted, meaning there will be less ecnhanting materials, meaning their value will rise. All the more reason to DE rather than scrap as an ecnhanter.