Painting Plastic

I hear of people painting tailights a perl color to enhance the image. But I was wonding the process in painting plastic, acrylic, or plexiglass. What I plan to paint is actualy the windscreen on m bike the same color as the bike. But I need to know how to prep if for the paint, if I schould sand it with a certain grit or what promoter to use. Any help would be great.

you can wetsand it with 600 grit and them use a adhesive promotor like bulldog. when i do them i only paint the outside too.