Plastic parts should be washed and Scotchbrighted with warm soapy water, dried and degreased, a light coat of a good quality plastic primer, the coated lightly in Satin black aerosol...and NOT Matt black, this will give you an OE finish, thatll look like it came out the factory like it.
Vinyl head linings, can be sprayed with vinyl specific aerosols that are available with the other products needed from Halfords..
Thom