Actually, this World of Warcraft gold making guide is very simple yet effective enough to bring more licenses to your bank in no time.
Going for limited supply items. Yes, you've heard me right. Purchase some of them from cheap NPC vendors and you're ready for a killing. You have an edge here because many people do not even know that they exist much more to find them.
These items are usually very cheap. You can even buy them for less than a gold. Next, run an auction house and jack up the price list to whatever price you like them to be.
Taking advantage of limited supply items on a timer. Items usually spawn every so often. Usually if you pick one, nobody will be able to pick another not until you make them available at your Auction House.
Here are a few techniques that I've personally used. However, it is best to look for information about what they are selling on your server before you even try them.
Elixir of Shadow Power. You can buy this item at Alchemy Supplies in Stormwind (Alchemy Shop to the left right after you entered into the Mage Quarter) and in Undercity (Apothecarium). You can usually buy it for 1g from the vendor. You may need to check your server how much they are selling. I've known people to buy at least 7g range while some others go over 10g, the decision is yours.
Free Action Potion. You can buy this as well in the Alchemy Supplies in Ironforge (Tram entrance) and Orgrimmar (Clef of Shadow). Cheaply priced at 18s and you can sell it on Auction House for 4g to 5g.
Those two options are good for low-level characters. If you are looking for World Of Warcraft gold making guide for higher levels, then you would need to do the following:
Frost Oil. Vendor Bro'kin at Alchemy Supplies in Alterac Mountains (can be difficult to find but usually found in the northern fall of the ruins). You can get it for just 25s and sell it for at least 5g and up.
If you follow those techniques, rinse and repeat repeatedly, you'll bank more gold in no time. Dominate the market by buying cheap items and sell them at any price you want. Simple but effective World of Warcraft gold making guide you can take advantage.