Here's something from my film school days that I've always found useful...

Regardless of whether you're shooting in studio or on location, have a light fill or light bounce board.

They're cheap -- I've made them out of cardboard and white paper before and that's worked nicely in a pinch.

The idea is that you have a white foam board or similar material that you can position and use to soften harsh light, fill in shadows, or direct soft light to the model.

This eliminates a lot of bad lighting problems.