The first thing you need with any business is customers (I call them clients, feels more high class). If you don't have people that will come to you then you have nothing.
Second is decide who your customer base is. Do you want to do dealerships and car brokers for $85 a car? $125 for a 2 hour express detail? $300, $500? How much do you want to make? What are you costs in time, labor, product, overhead? Figure all that out and you will have an idea of what to charge.
Look into tint, wraps, clear bra, and chip repair. If you can't do it farm it out to someone reputable who can.
Go to car shows, hand out business cards, talk to people. Get a good logo, website, facebook page.
Over the last 2 weeks I have been doing more and more high end cars (Porsche, Ferrari, Lambos), and it is all about the people I know. The average ticket has been around $1300 for no more than 3 days of work. A good detailer can do a standard detail with one pass of paint correction on a moderate vehilce in a day (7-10 hours).
If you are just starting out plan on doing a bunch of crappy soccor mom cars with cherreos, french fries, cigarette smoke, and all kinds of nastyness. The high-end stuff will come later.