If the paint is still in good condition and not peeling I just rough it up and bit and paint any automotive primer. Stay away from spraying acrylic paints in a can as they can react with some common lure paints. I use a cheap auto primer in a can that you pick up from hardware stores. If its on bare plastic I would use a plastic/bumper primer first that you can buy from either a hobby shop or auto store.
If the paint is in bad condition I bead blast mine, a lot less messy.