It's a myth that there is a special trick or technique to successfully photographing people with dark skin. While dark skin may blend into a dark background, the same is true for black hair on a person with pale skin. All good photographs depend on the effective use of light, and an experienced photographer actively manages the light, rather than leaving the results to chance.
Understanding Camera Metering
No matter how complex light metering is in your camera, each sensor evaluates the light reaching it as though it is seeing an average scene. This average scene has about the brightness of a value called 18 percent gray. Any scene that is, on average, lighter or darker than the 18 percent value will require an exposure adjustment. This will have an impact if a subject's skin is substantially darker -- or lighter -- than the middle value.
Recognizing Exposure Adjustments
Exposure adjustments seem backwards to novice photographers. Shooting a snow scene on a bright day seems like a situation with lots of light yet, without adjusting the exposure, the photo will seem dull. The camera adjusts for average brightness, making the snow gray, so the photographer must give more exposure than the meter suggests. Similarly, if a subject with dark skin occupies most of the camera frame, such as in a closeup portrait, less exposure is needed, because the subject is darker than the 18 percent brightness average.
Adjusting Camera Exposure
A digital single-lens reflex camera permits the greatest manual control over a camera's exposure. Most DLSRs have an exposure compensation setting that adds or subtracts up to two stops on the meter. Point-and-shoot cameras don't have this flexibility, but using an 18 percent gray card, available inexpensively at most camera stores, forces your camera to expose for light conditions, not the subject. Have the subject hold the card in front of her face as you depress the shutter button halfway, then have her lower the card. The camera will retain the exposure for the grey average, and skin will be properly rendered.
Direction of Light
Nothing screams "snapshot" like the look of a camera-mounted flash on a subject's face. This effect is aggravated with a dark-skinned subject, as the background is usually dark too. Proper exposure is a start, but using auxiliary light on your model is necessary to define detail and separate your subject from shadows and dark backgrounds. Managing light may mean moving the subject relative to the light source, if you're using available light such as a window, or moving lights themselves, as with a photo studio. Using reflectors opposite the main light in either case is a great way to direct light back to the subject, defining dark-skinned features.