The first and best way that I found to market was online. I would put up ads on craigslist and then link them together.
Here is an example. That is just one page. Anyway, I build 4 or 5 pages and then go back and link them together so that no matter what someone searches for to find my ad, they are still able to see all the services I offer without leaving craigslist. It has worked out so well for me.
Word of mouth is the next best way. I do that by leaving business cards with my customers to hand out to their friends. I've also been known to leave them with some vinyl stickers with my website URL on it that they have put in their windows to help me out. I'm always surprised how many people do it, but every now and then I'll see one of my stickers in a window and recognize it as a car I detailed.
I am also a huge fan of local car clubs. I detail for the local Integra club and Supra club. I make it a point to organize detailing days and show & shine events for them. That has helped generate referal business a lot.
Having a website helps quite a bit too. You can't always show everything that you can do on a business card, so having a website that they can go to helps. I am (still) working on mine, but it should be done this month>.
I'll have to come up with some more. I know I've got some good ideas in here somewhere.