Outside: Natural light is always the most optimal. However, certain sun angles can cause squinty eyes, harsh shadows, and large white areas in the image. Either position yourself with the sun behind your head or try standing in the shade.
Inside: Use natural light coming in from outside by taking your scan while facing a window or standing in an open doorway. If you can't find any natural light, try experimenting with different lamps and overhead lights. Lightbulbs can produce a variety of color temperatures ranging from white yellowish to blue, so do some trial & error, and see what looks best!
If you would like to adjust the tone, please use the skin tone adjustor located in the render preview screen. The "+" button will make it lighter. The "-" button will make it darker.