wipe w/ wax&grease remover
carefully sand it
wipe again
primer it
paint it
lightly sand it again
paint it w/ final coat
=Good method
clear coat if you want...get a flexable clear coat.
Be sure that you want the color there FOREVER becuase you will not be able to remove the paint. The paint remover would eat the plastic too.
oh and get color match paint from
www.paintscratch.com - perfect match...paint in a dry/controlled environment like the basement - humidity will ruin the paint.