A good polish to clean plastic is a German product called MER. Not cheap, but really brings plasics, like that used on a Caravan for instance, up a treat.
If you have scratched plastic, another good product is 'Novus' V.Expensive for its size, but will remove those disfiguring type scratches for instance on a cabinet, transparent screen, mobile phone case & display area, etc easily. Its a 3 stage product.