Well, seeing as you're going for a lineless approach (at least, that's what it looks like), you should probably elaborate on Warbrain's answer. Make a new layer above your sketch, and lower your sketch's opacity, then trace the lines (it doesnt have to be a really refined sketch), block in your colors, and paint from there.
While you're at it, you can use your hands or stock photos to get the anatomy down. Your painting may be great but if the anatomy is off (or vice versa) then the result will be unpleasing. :)
(since I can't attach pics from my ipod...) Reference