When designing characters, I think it would be a good idea to apply your knowledge of composition. Use your knowledge of contrast, economy, rhythm, emphasis, balance, and movement to make sure your character is being viewed the way you intended.
A very simple example is, in most cases you want the face to be the main focus, so you make sure there are directions in his design, rhythm, emphasis, and contrast to lead your eye there. If you find that other areas are competing for attention, it's easy to tone them down, to bring the focus back to the face!
I'd also recommend reading up on colour theory, and maybe even do some master studies of artists whose colours you like and want to emulate!