Knowing how to make gold in world of warcraft is a real life skill integrated in the game. It reflects real life economics of buying low and sell high, be that a luxury, commodity or essential item, food or anything that is needed in the game by the 9 or so million players logging on wow worldwide. There are many, many ways to make gold in wow. The most common are to use the auction house, gathering items that can be sold to vendors or preferably sold at auction, making money from professions, and lastly good old fashioned grinding.
Making money from the AH (auction house) is easy. Just use the search button to scan prices in the auction house and sell your items for the best price you can get to make a profit. To do this can be fairly time consuming and many players tend to do this almost full time as they have little time to do anything else. However this can be made easier by using the auctioneer add on to scan prices giving you a good idea of what prices are like on your server and enable you to undercut other players so you can sell faster. Or use it to find items that are greatly under priced so you can re-sell quickly at a profit. The best thing you can do is to always make your auction as short as possible, like Buy wow gold two hours, at times when the servers are busy like in the evening when everyone is at home.
Skins you can trade for considerably more at the auction house rather than vendors because you will always have higher level players who have lots of gold and will pay for skins to create armor etc, rather than go out themselves killing the mobs. And anyhow they use the skins to make far more valuable items than what they pay for the skins. In fact they pay for the convenience of not having to do the skinning so it is a win win situation.
Fishing is the other great profession for making gold in wow. On a few servers quite a few players make up to 300 gold an hour without any problem. Besides it’s not just fish that you can catch but also valuable items like blue and rare purple items that you can very easily re-sell at the AH for hundreds if not thousands pieces of gold.