Take a photo where there are two light sources. Tip: they don't both have to be active sources of light (light bulb, sun, candle, etc). One could be a passive source - where the light is reflected back onto your subject.
We parked in a parking garage to use the overhead florescent lights, and the car's headlights to light me. Notice the greenish tint to the light from above, and the orange light from the car's lights.