A quick post as I am knee deep in work. Here are two single light techniques that tend to work well. The first is a Rembrandt technique which results in a heavy shadow on part of the face with a triangle of light on that side of the face. You can notice I don’t exactly look thrilled in that shot. This is because I find it tedious to setup which means I probably need more practice at it. Seriously though, it can be a challenge to do but it worth the effort. To set it up your light will be slightly higher than your subject and just off to the side. You want the light at about a 45 degree angle to your subject aiming down that is. But some adjustments will be necessary.
The next shot is a bit easier and called the butterfly technique. The butterfly is the shadow formed under the nose which tends to look like a butterfly. The light is close to overhead and directly in front of the subject. This is one of the easier single light techniques and is one of the first ones you might want to get the hang of.
In both cases, you can complement it with a reflector to fill in some shadows on the dark side of the face but don’t over do it so much that you lose the effects that make these what they are.