if you want a great finish you will need:
Scotch bright 7448 or 600-800 grit sand paper (for initial keying of surface so undercoat adheres)
Spray undercoat for plastic/bumpers
Car/Auto spray Paint (in the UK I've used U-Pol brand)
Car/Auto Spray Lacquer
Optional if you want a super shiny/flawless finish:
1500 grit sandpaper
T-Cut/scratch remover
Lint free cotton cloth
First use the scotch pad/sandpaper (600-800) to key/prep the surface so that it's uniformly marked.
Then use a damp lint free cloth to get rid of any debris.
Allow to dry or use a dry lint free cloth so that no moisture remains.
Lightly spray the primer at a distance of roughly 30cm until evenly coated.
Wait until it is dry.
Apply paint lightly at approximatly...