There are as many ways to earn gold in World of Warcraft as there are players it seems.
Everyone has a gold secret they claim is "The One" that will make you millions on WoW.
Well, I have my own gold secrets, but really, they're not secrets.
Here, I'll share three of them with you, so you can use them to see an increase in your gold fast.

1. Pick up grey items.
   This might sound foolish, but grey items can and do sell well to a vendor.
   That 33 copper collar doesn't seem like much, but compared to that 1 copper spider leg, it's a fortune.
   As you get higher up, focus on the things that sell best.
   Items that stack are usually better to carry than things that don't, a stack of 20 paws that sell for 25 silver is better than the 1 skull that sells for 75, as long as you have more than one.
   If you're low on space, remember weapons sell best, followed by gear, then various stackable items.
   
2. Make sure you have at least one gathering profession.
   Gathering professions are the meat and potatoes of WoW.
   You might only gather that iron ore, but someone might buy it from you, smelt it down, and make a dagger out of it for an alt.
   Or that Northrend herb might go into a flask a raider needs.
   Not a cook, but like to fish? Those fish are valuable to the right people.
   
3. Auction House what you don't need.
   This sounds like a no brainer, but you can make a lot of gold in a short amount of time there.
   If you have a gathering profession, sell off your extra.
   Pick up a green or blue item in a dungeon that you don't need? Put it up.
   Find out you have a couple stacks of cloth, or you're a rogue with a few mana potions? Throw them up.
   You'll be amazed at what people buy, and it clears out your bags for more important things.
   

The more you play, the more gold "secrets" you learn.
These three might help you earn some fast gold, or at least easy gold, and keep you in comfort while you venture around Azeroth.