1. Do your own research. Everyone who makes good gold from AP has. TTC will help you get a sense of which items from the Golden are worth buying and which are not.
2. Don't tell everyone. It is imperative if you want to make gold from AP that you don't go around telling everyone and their mother what items they should be buying. You want to make a good kickback on your AP gains? Then it should go without saying that you don't want the market to become entirely flooded with those items you've decided on selling, because that will make those items entirely useless for you to purchase and list for gold in the first place - ergo, don't go around handing that information out like candy on Halloween.
(2b. Above point also goes for "good mat farming locations". If you keep your wits about you and find a good place to farm, don't write guides about how awesome those places are, because that will make your place entirely awful for farming instead.)
3. If you follow the steps above you will have two advantages over other traders; knowing what to purchase (and where to farm), and how to not sabotage your own trades!
4. Profit.