It took me a bit before I learned this. Crafting does not earn you income at the low levels. There are a few recipes that may be profitable, but on the whole it is vastly better to gather and sell than to craft when you’re going up through the levels. I was killing myself mining and blacksmithing, turning out complete junk. Finally I gave up and started selling the ore straight, and suddenly I’m swimming in gold. I still work Mining up, and when I’m up a few more levels it won’t be much work to boost Blacksmithing up to where it actually produces worthwhile stuff.
I find Jewelcrafting to be fairly profitable, but again you’re usually better off selling the ore instead of the jewelry.
Two gathering professions (usually Skinning plus Herbalism or Mining) will net you solid income, and you should have 40 gold well before level 30.