There are a few things I have found to make any 3D artwork better. The first and most important thing I have found is making sure items and people that should be casting a shadow just that. It grounds the person or object and makes them appear more real.

The second item I find important is reflections. Reflections can appear in objects all around us, why not include them in your artwork.

Please feel free to critique this and add some ideas of your own.