Clear out the garage and make sure there is ample room for you, your equipment and your subjects. At minimum, you will need approximately 15 feet between your backdrop and you. The garage will need to be wide enough to accommodate your background and lighting equipment without being in the shot.
Check the electrical outlets. You may find that your power supply is inadequate and may need to call a professional electrician to add outlets and verify that the wiring in your garage can handle your photo equipment. This will prevent a blown fuse or flipped circuit breaker in the middle of a shoot.
Seal the floor to prevent rising vapor or water. Skipping this can result in a damp atmosphere and water damage to your equipment.
Paint the interior of your garage a neutral color. This will prevent a color cast from forming on your images. Bright colors will reflect light, and darker shades will absorb it. A neutral-color wall can also double as a backdrop.
Mark a "subject spot." This is where you will seat your portrait subject. It should be approximately 5 feet from the background and 8 to 10 feet from the camera, depending upon your lens and the pose.
Set up your equipment. At minimum, you will need a background light, main light and fill light. The number of lights may increase based on the size of your garage. You can also modify the type of light with reflectors, soft boxes and umbrellas, allowing you to add variety to your lighting styles. Other accessories, which are optional for outfitting a portrait studio, include stools, posing blocks, backgrounds and props.