You've got a pretty good idea of what you're doing. I've given you something to go off what Glak was suggesting.
Defining your light source is very important, and when everything in the image reacts to that light source it will give a lot of depth and shape to your characters. When there's an element in an image that should be producing light but there is no light bouncing off other objects, the element begins to feel as though it doesn't exist properly in the world you are viewing. This is just as important when dealing with shadows.
Despite his skinny right (our left) forearm and the tail of his robe, I didn't change his overall shape, only the colors and lighting being applied to his person. I did change the fireball and his eyes but that was kind of just fun...
The number of colors can easily be reduced but I hadn't bothered to do so. Just remember contrast is your friend, the dark parts on his robe were almost the same color as the base color.
Give the lighting more of a tweak and see how you go! Good Luck!
