My business is not detailing persay, though people often think that's what I do. I do automotive reconditioning which includes interior repair, re-dye and sometimes cleaning, exterior graphics, moldings, windshield repair and a few miscellaneous learned tricks to make a buck. I've started this business in 4 different locations, 3 of those times successfully. So I can at least advise with a few good poiinters for starting these types of businesses.
1. As has already been alluded to...do the research. Make sure your approach and location and services offered matches where you're thinking of opening business. Make sure there is not a flooded market there. That's where I went wrong the one time mine was not successful.
2. Be as prepared as you can be before you start, meaning you've got a reasonable amount of start-up equipment and stock of supplies, business cards, dependable vehicle, etc. Try to think of everything you will need, from extension cords to invoice books to all the types of cleaners and polishes and cloths to tools big and small, buffer, compressor, etc. And have them as organized as possible with the most commonly used things the most accessible.
3. Definitely do the business license (will have to do the name search to make sure that name is not already taken in your area, state, etc.) So then you can open a business bank account.
4. Do enough research to set your prices right. Usually correct pricing is based on A. The competitor's prices and B. What you need to clear a comfortable profit, taking into consideration mucho overhead (always more than you first think it is). If you feel your work is far superior to the competition's and you can therefore charge more, then you may need to come across more organized and professional in order to justify the higher price. Many in these trades did not start out charging more, not until their quality of experience and accumulation of accounts put them in demand to justify charging higher prices. (I'm sure there are exceptions to that). If you set your prices right around where the competition's is or just slightly below, you give yourself a better chance of gaining new accounts and later down the line you can raise your prices just like every other company and service does eventually.
5. As has already been stated, the business will not come to you. Whatever your approach, the main thing is to get out and make yourself and your services available. That does more for sales in these types of businesses than almost anything else.
6. Think bigger than you are. Don't talk to prospective accounts as if you are just a couple of guys out trying to see if they can detail a few cars for money to pay their bills. No, now you will be a legitimate business just as legitimate as General Electric or Microsoft or Chevron. Get used to terminology that represents yourself as a professional company offering services for clients with the need to schedule appointments and pick up their car at a certain time, be charged the applicable taxes, etc, etc.