I'd say work on lighting, flow, and work on your sigs longer. When you start out, everyone pumps out like 5 sigs a day, but that's not how you get better. Find some good tutorials, quite a few of us GIMPer's have good tutorials, so I would check out the resource thread.
Gah! It hurts my eyes! Get a better background and blend the render more next time. Gradient maps can help with that.