As in kids' furniture, or outlet and switch-plate covers
Prep: To ready the surface, wipe with an ammonia-based cleaner, rinse with a damp cloth, and let dry. Rough up glossy or previously painted plastic using 150-grit sandpaper so that it will more readily accept the new paint.
Coat: Apply a bonding primer designed for plastic, and coat with latex paint. A wider brush covers in a few passes, minimizing brushstrokes. If you're not confident about your brush technique, try a 4-inch foam roller or a spray paint made for plastic.