The only real tip I can give is to lump colors and shadows into a couple very vague groups, the high, sometimes the mid, and the low. Just separate the actual depth and shadows into those categories and tweak it till it works!

It's all a matter of personal style, and my influence from comics and animation has shaped the style I've come up with. So, do your own research and find out what works and what doesn't!

Best of luck!