Photographer Joe Edelman posted an awesome video tutorial a couple of years ago where he likened shooting a portrait photo to lighting an egg. After drawing a very happy face on said egg, he moved a light around but didn’t move the egg at all. By doing this, he was able to figure out how the light will look on the subject when they are photographed. This is much easier to do with a constant light than it is with a flash, but the concept can still apply.
The tutorial is much better illustrated in the video presented after the jump.