It's really finding something that works for you. If you want to spend lots of time flipping or farming mats to sell then you can do that.
I find niches, it doesn't give me some huge income but I make a good amount and it's more interesting than being a mat factory. My latest was building mainhand's for the level 53s with the craftable artefact upgrades I've REd.
Someone has found my items and is trying to flip but he's charging 4x buying the mods separately so I don't think he'll make much