How do I paint on plastic?

Thanks I could spray some parts but others would have to be by brush so I’ll try both. And tricks or suggestions - should I lightly sand first?

You could try to use a very fine grit sandpaper to get off any sort of finish that may be left on there. That's always the hardest thing about getting things to stick. Also, do very light coats and give it enough time to dry in-between coats. One more thing, pay attention to the temperature suggestions for the paints. Some paints have suggestions for temperatures so that the paint drys/sets better and I have found that this really is important.