Right now, just about all new business that I pick up (besides word of mouth) is coming from people searching and finding my website.
A website is very important, especially if you plan on doing something full time, you need to have a professional business presence and a website is an important thing to have these days. Right now I use Intuit and just threw something together using their site builder, which is very easy to use. My current site isn't the best, but it's much better than nothing. I plan on having a more professional site made by a pro designer very soon, which I completely expect to improve my business as it will look more professional and have improved SEO to help people find the site.
Once you have a website, I'd look into Google Adwords to drive people searching on Google for a detailer in your area to your site, it's worked really well for me.
In the past I've done newspaper ads, ads in car show programs, craigslist, an ad at a local gym on their big screens - none of these worked, all a waste of money. Well except craigslist, that was just a waste of time since it's free.
If you have a local Chamber of Commerce, join that and network with other business owners, good chance you will get business from them and you can cross market your services with others such as auto repair shop owners, car audio store owners, etc.
Once you gain some good customers, always ask them to refer you to their friends and family. I tell them I would really appreciate if they would tell others about me as being a small business owner I can use all the word of mouth I can get, they are usually more than happy to do so. Maybe offer a discount on their next detail if they send you a few people.
Hope this helps.
