i always use Meguiars nxt stuff its quite expensive but worth it i reccon always birings a good shine up
for any marks i use T cut polish i think it says its for new cars etc but its not as harsh as the normal stuff
then i just wipe the dash with some dash wipes and give it a vacuum once a yearÂÂÂ

we have some stuff at work called demon wax apparently all you need to do is spray it on mixed with water and it does the job
sounds too easy to me
