I would use an upholstery shampoo. Strongest smelling you can buy. Don't forget the ceiling and floors,seatbelts etc. Clean all glass etc then febreeze every night when not using. Wherever possible open windows. Nothing is better than airing, you can clean as much as you like but if you don't air it loads you will never get rid of smell. Will prob take a couple of weeks to get rid of smell, it's not possible to get rid instantly.
Just borrowed a car for 2 days to test drive. Perfect for us - except... a smokers car. Won't take it unless I can get the smell out. Remember we rented a smokers house once and despite steam cleaning twice, air fresheners etc it always smelt. Just read a post where a lady tried bicarb, airing & vinegar on her pram and it still smelt. Anyone got any other ideas or is it pretty much going to be a smoky car?