The vanilla WoW Horde leveling guide you see on this site was originally made back in 2006 by Joana (AKA Mancow, or FuriousPaul). The guides have been tweaked many times over the years to make things "faster". The leveling guides were made because of all the messages I got from people asking me how I was able to level up so quickly on new realms. I was first to level 60 on 7 different realms (3 with Mancow and 4 with Joana), even winning Blizzard's "First to Level 50" contest they held back in 2006.
The problem currently is that a previous patch introduced a much smoother paced leveling system, though it was definitely slower. Many actually enjoyed the tweak to the overall progression system but ever since patch 8.0 went live, many MMORPG lovers are reported that is unnecessarily difficult to level through some of the older content drops, which was an unintended side affect according to Blizzard.
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By constantly doing quests, you will experience a very different game than if you just level through pure grinding. You'll be out there making a contribution towards the Alliance or the Horde. Doing these quests takes you through the heart of the game's story AND provides the fastest rate of experience. Have fun in World of Warcraft and enjoy developing your hero - your adventures will gain you great reputation amongst the land.
I used fully upgraded and enchanted heirlooms; missing only the fishing ring. Leveling from 1-20 took ~3 hours, at which point I immediately turned on War Mode for the duration. I rarely encountered enemy players, and when I did they almost always left me alone. But the few times I did get ganked, the total cost in time was insignificant. Maybe a total of 5 deaths from ganks in the entire 40 hours.
Another dungeon farm, this time in Uldum, Tol'Vir trash mobs drop loads of embersilk cloth. Stacks of this tend to sell for a tidy profit, though prices vary depending on the realm. A typical clear of the dungeon takes about 5 minutes, netting about 7.5k per hour in cloth, vendor trash, and various other drops like mats and BoEs. Pick up a Potion of Treasure Finding and farm to your heart's content! It's just as profitable on normal mode as heroic, too, making farming all the quicker and easier.
One useful data point is the cost of gold from illicit services. The WoW Token has taken a bite from their business, but these people are still out there, botting trade goods and stealing and pillaging accounts despite Blizzard’s continuing attempts to ban cheating accounts and confiscate illegal gold. The going rate for gold from these outfits is about $15 per 100,000 gold.
If you want to spend as little time on your alt as possible - just do Legion Invasions. You can use sites like (https://wow.gameinfo.io/invasions) to track when the next invasion will be. Log in, fly to the closest world quest, and once there - right-click on the quest's name in your quest log and "Find Group". Sign up for some group, or if there's none - just start your own immediately, and people will come to you. It is 10 times faster to do invasion quests in a group. Once that particular quest is complete - leave the group, and fly to the next one, where you should find another group. Don't expect the group from one world quest to follow you to the next. Then you simply log out until next invasion. You can do 1-2 invasions a day, and each invasion will give you about a level or 1.5 of experience, if you have full heirloom gear. Each invasion will take about 20 minutes.
Although WoW currency can be found through quests, fallen enemies or the dreaded "farming" process, doing it the conventional way is time-consuming. Considering the upcoming release of the Legion expansion pack in August of 2016, stocking up on gold is more important than ever. This way, you can spend less time farming and more time buying everything you need to tackle the next set of challenges.