Instead of starting at the bottom and making the shading darker as you go up, try making it look dark at the top and bottom.. I would suggest looking at skins on pop reel and looking at how some people shade without copying it.
Shading would help a ton, your first attempts at shading might be sloppy and turn out bad, but it will get better eventually. Look at other peoples shading on their skins, dont copy the exact shading though, and create your own style.
