Set up your stage lights in a triangle formation around the subject to be lit. Place the background light behind the subject and set up a key to fill light in front of the subject to the left and right. Set the lights above or below the subject, aiming upward or downward as needed. Connect the lights to three separate dimmer switches on a lighting control console.
Affix cellophane color gels as needed over the opening of the lights. Attach to the outer lip of the aiming dome. Keep the gels taut and out of contact with the light bulb to avoid them from melting.
Set the stage lights to varying relative brightness for different effects. Keep the fill light at a brightness less than that of the key light to achieve some shadow definition on your subject. Set all lights to high brightness for a high-key, lighthearted effect appropriate for sitcoms or daytime scenes. Set the key light to a bright level and the fill and background lights to dim (or off) to create a heavily shadowed effect appropriate for suspense, horror or nighttime scenes. Light from the background only to achieve a halo effect around your subject.
Use stage walls or other obstacles to create specific shadow effects. For example, you can cut a window into a stage wall, affix blinds and set up a light behind it to create the illusion of a dark room being lit from the outside.