Autoglym for the metal work, Armourall tyre foam for the tyres ( will also do black bumpers as well), a good glass polish/cleaner.
As for the interior a good vacuum now and then and wipe the dashboards with a damp chamois wil do.
Wouldn't do the floor mats with anything - anything that would bring them back to black would leave them slippy and you risk your foot slipping off the brake pedal.
Just give a hose down and scrub.