[Mike McCarty]

My suggestion would be to become as familiar as you can with the environment that you are bringing your model into, regardless of their skin color.

Practice in this spot with stand-ins as often as you can and make note of what works during different times of the day.

It would be helpful if you could adjust the white balance on your camera and have the ability to spot meter the subjects face, but if you can't then the next best thing is to try different lighting set ups before the model gets there.

There may be special considerations for dark skinned subjects, reflecting light into the shadowed side may be a little more important, but I think that if you set up good general lighting conditions you will get a good image regardless of their skin color.

Here is a photo I took a few years ago that is showing some wear from a poor scan. I took this with my old film camera (remember them?). I'm pretty sure that my digital camera could help me do a better job today of managing the light. I don't think I did anything particularly different because of her skin color.

Others may have more specific suggestions.