hmmm this seems kinda reminiscent of Splat Pixel, inspired by him perhaps? Not blaming you of ripping or anything, just random musings. Anywho, I think the best step for anatomy,is to pull out your trusty pencil and sketch, and buy yourself a nice anatomy book. I always find it's easier to learn basics in art, with a tool in your hand other than a mouse, but that could be just me. As of now, your shading seems a little pillowy, and there is also a relatively small range of values. I would suggest introducing adding some more drastic darker tones, a dark brown, or even black. This can help make the piece more dynamic and interesting.
