to do it right involves a bit of Broker knowledge. Take a look at your designs, than look up what you make with them on the Broker. Judging by how much your mats are worth and how much the end results actually sells for you can get an idea as to whether to craft that item or not. Like as for me I never crafted level 15 weapons unless someone needed one. Instead I crafted Devious Spears which for awhile were selling well until everyone began to make them. (Guess Ectoplasm fragments aren't so uncommon after all)