This tip is bleeding obvious, but most people don’t use it, myself included, very often. Are you making this mistake, too?
When we have a non-gathering profession, we are often so focused on leveling up that we forget our primary goal with the profession: Making gold.
We tend to only create items that give us skills, i.e. the green, yellow and red ones, so we rarely go back and create a now grey item that made us money.
Of what use is it that we can create some very expensive boots with frost resistance and other things, if people want a white shirt? Or the lovely red dress, you see on the picture? This has been known to sell for 50 gold on our server, and the mats to make it with cost almost nothing.
Make what people will buy, and then make things that improves your skills. In this way you can make gold with your professions.