Well, I can tell you that you won't be getting much from this size resolution. If your adamant at keeping the character around that size, consider changing the size of certain body parts, like making the head bigger and easier to work on and identify.
I also noticed upon zooming in that there was very minor shading, and I can tell you that the colors need more contrast, as you can barely tell them apart. If your concerned about the color, I would advise you lookup a bit about color theory. I'm no expert at it, but it seems that your palette is unsaturated and a bit dull. This is COMPLETELY fine, but I wanted to know if you'd want to try something else.
I also don't think your thinking about lightsources. I can kind of identify a light source from the bottom left, but it would be a bit easier to have it from the top left (though thats' just my opinion.) You could try to consider folds in the clothing as well as well as antialiasing to make it appear nicer.
Before i make any more changes, i was wondering if this was was a top down sort of sprite. One more thing is that certain outlines aren't smooth, and I'm not certain why you made that choice.
And finally, I made my edits as if he was fat. Is he?
