I use Zymol's Clear product, in a very weak solution applied with a cloth. Then after that has dried and plastics been in the sun at least 15 minutes I use Zymol Vinyl which you must apply in modest amounts or the car's plastics will go too shiny for my tastes. Once finished I the pass a damp cloth over the treated plastics again. Sounds OTT but in practice the products are so good you don't do it best often.
I use
www.vertar.com in the UK to supply Zymol, or buy loads in one shot and get it delivered to a local USA address if I'm across the pond.