a big business for your workers while you get nothing.
people will need a way to know you offer car wash business. if you have a good location, advertisement could be as simple as having the first few sets of cars come in and washing them. once people see these cars, they automatically know there is a car wash there.
you can also put up a sign/billboard that says you wash cars. word of mouth works wonders too. the rest would be up to how professional you are in your service delivery. if you are the best car wash in the neighborhood, just relax and count your money because people will always 