This needs an anatomical overhaul. My grasp of anatomy isn't perfect, but I did a quick sketch to highlight some issues.
The different parts of his body all seem to exist independently, and they don't connect in a natural way. The shoulders and arms should flow into one anoter, as should chest to shoulders, abdomen to groin to legs, etc. Though the legs clearly weren't mirrored, they seem to point in opposite directions, which puts him in an uncomfortable, if not impossible, stance. Given the direction the rest of his body is pointing, his left (our right) leg should be turned more towards his right, as should the left foot. His hands are also radically different in size, which gives a strange impression. I shrunk his head somewhat; probably way too much. Your head size isn't necessarily wrong, but I assumed you were going for normal human proportions, and adjusted its proportions with regard to the length of his arms.
It would help you a lot, I think, to spend some time practicing on paper with reference to life, photographs or an anatomy book, and throwing down some rough sketches before attempting this in pixels. Not to sound discouraging or hypocritical, since my own grasp of anatomy is far from perfect. it's just that, regardless of who it comes from the fact of a firm grasp on these kinds of things being elemental to artwork in any medium remains true.
