I think you've got some great linework and body shape going on here, but as for color, I'd recommend starting with a basic new layer, and mark off the areas where the shadows are with a darker skin tone, typically by sliding the color slider down and to the right just a bit. Zoom out, and see how that looks, and play around with the layer opacity and layer style, like overlay, multiply, soft light, etc. Once you find something you like, either rasterize or select that color, set your layer to normal, then fill in the space with that new color, and use a brush tool and blend with a soft brush. That should do the trick.Do the same with highlights. Determine if you want the highlights to be emphasized, or subtle. I'm not a "master of art" but I love to give advice, even if small, whenever I can. Feel free to reach out on twitter