Even the most interesting video will fall flat if the audience is distracted by bad lighting. Here are some quick tips.
The main light source in your shot is called the key light, and in a basic shot this light provides most of the illumination. Unless the intent is to create a dramatic effect like strong shadows across the face or a silhouette, the key light is usually placed beside or slightly behind the camera.
With the key light providing most of the illumination on your subject, that strong light will almost always cast some shadows on the opposite side of the subject’s face and body. In order to reduce the depth of those shadows, another softer light is often placed to fill in the darker areas, giving it the name fill light. You don’t want to eliminate all the shadows—if the light is too even, with no contrast between highlights and shadows, your subject will look flat on camera.
While the key light and the fill light are generally placed in front of the subject, the rim light sits behind the subject. The purpose of the rim light is provide some definition to the edges—the rim—of your subject, visually separating them from the background elements in your shot. (Picture the thinnest crescent moon—the sun is functioning as a rim light, helping the dark moon stand out from the black background of space.) Your rim light doesn’t have to be very dramatic—just enough to make the subject pop.
Go with your instincts
These are general principles, but you should always evaluate the shot as it looks to your eye, and more importantly, in your camera.