Vacuum the rug thoroughly to remove any dirt on the surface of the rug or trapped in the fibers. This is especially important if the rug has been outside and exposed to the elements. If the rug is very dirty, spray it clean with a hose and hang it up to dry completely before you vacuum.
Paint the base color or the most dominant color in your design onto the rug using a flat interior enamel paint and a paintbrush. Let this color dry completely before you start adding other colors or the paint colors may bleed together.
Touch up the base coat of paint if necessary after it has dried. The rug may absorb some of the paint, leaving areas looking faded or lighter than you desire.
Add detail to the rug by painting one color of interior enamel paint at a time with a paintbrush and letting each color dry completely.