When shooting outside, there is usually only one source of light: the sun. But there can be other light sources. For example, if the sun is reflecting off of a lake or other surface (snow, for example), light may be coming from more than one angle. And if you’re doing night photography, you might have light from the moon, flashlights, headlights, or other light sources to reckon with. And don’t get me started when it comes to indoor lighting!
Once you have determined the main light source and the direction of its light, look around for other light sources (reflections, etc.) What direction are they coming from? How does this affect your photograph?