Well, the step left and step right animation will make him slightly shorter. This is due to your elevation changing when you elongate your legs and then apply mild exaggeration to it (a part of the animation process) So we know his body will be one pixel lower in his stepping frames.
Secondly, his arm should start to go behind him/his back, and the arm going back should become a dark shade due to the light no longer hitting the visible surface. The shape of the arm will become smaller due to perspective.
The same goes for the opposite leg.
Also, his feet are facing to the side while he's facing forward. This makes animating the feet a lot harder. Try removing the black pixels on the outside of his foot, and put a dark shade of the shoe color on the outside of the foot. This will help make the foot look less square.
Also, with these principals in place, consider the changes you'd see from his hand/leg swinging forward.