You must prep the entire surface of what you are painting. You must then mask areas that could potentially be damaged by sandpaper or scuff marks (grilles, door handles, chrome trim, rubber trim). Don’t remove something you want to paint, though. The very first step is to remove as much of the vehicle’s hardware as you can (i.e. Since prepping your existing paint is so important, we will cover it in some detail. This article tells you basically what you need to do if your paint is already in good condition, but you want to add a special effect pigment custom paint over existing paint.