Sand out any imperfection first, if none use a red scotch-brite pad that you can pick up at any local body shop or store and scuff. Your going to want to wet the part and sprinkle Comet believe it or not on the part to help as a contaminate remover so that the paint will adhere properly so the plastic, fish-eyes are a pain in the balls...lol. Im not sure if your painting them or not but if you are make sure to hit it with some wax and grease remover (PPG makes this) and use Plastic Adhesion Promoter(Also another PPG product). When your ready hit it with some sealer that is close to the darkness of your vehicle followed by a few layers of basecoat and then 2-3 coats of clear.