Wash, de tar using AG intensive tar remover or tardis, this will get rid of the worst of the contaminants, use either the Meguiars or Autoglym clay kits from halfords if it's your 1st attempt as it has everything you need. spray a small section of each panel with quick detailer, warm up the clay and lightly rub over the surface with regular folding to a clean surface, wipe down with a clean cloth. Then move onto our polish / prep / wax or sealant etc