Besides what Steve Lenze has mentioned, consider the lighting. You currently have 4 light sources: 2 equal sources of light from both left and right directions, 1 direct front facing light source, and one from top right of the image (left of character). While having many light sources is not incorrect, it is quite complex. If you decide to keep them, you have to make sure that the shadow shapes are designed as per the lighting conditions. An easy way to approach it is as follows: Set your first light source...outline the shadow parts of this light Set your second light source...outline the shadow parts of this light Repeat for other sources of light... Where these shadows intersect will be your darkest tones, and where they do not, become affected by the other light sources, hence making them brighter. Keep it up!

Find the gesture, then build the structure for your figure. Muscular figures can look kind of stiff if you don't create gesture first.