Some manufacturers make paint for the specific application... Dupli-color is one that has paints designed for bumper covers and plastic trim, but I'm sure that others are available. As with any paint job, preparation is key. Follow the paint manufacturer's recommendations, but you generally want to evenly scuff the surface for improved bond, clean the surface so it's free of all dust and oils, prime, and paint. Something else to remember is to take your time... multiple smooth, even, LIGHT coats will typically produce the best results. Hope that helps some.