Anatomy is not something that comes easily. It takes practice and repeated attempts to nail it down.
One thing I suggest is gathering yourself a whole bunch of reference pictures of the subject you are trying to illustrate and try sketching out the pose it is in a couple times. Doing this allows you to get a feel of that subject's body structure and how it meshes together. You'll come to find that your proportions will suddenly start meshing well together.
Once you start getting the anatomy down, you can try your own custom poses.
At the moment, I really don't like the coloring technique used, but that's only to my eyes.