As is the case before painting any type of material, the surface must first be washed. However, it is extremely important to use a cleaner that is designed specifically for vinyl and aluminum siding. There are several good brands of paint on the market, but what is most important is to choose a paint that is labeled all-acrylic. As you know, vinyl expands and contracts more than most other sidings. If the paint applied over the vinyl siding cannot expand and contract as much (or at the same rate), it will not adhere and will peel and chip off over a short period of time. An all-acrylic paint will move with the vinyl surface. You will, however, need to apply at least two thin coats, maybe more, as thick coats of all-acrylic paint will not hold well on vinyl siding.