I just took my business full time about a month ago due to being laid off. So I'm sure that others will be able to give you better advice.
So far I've kept pretty busy, however with the holiday my schedule died out almost completely. Last week was very slow (only 3 details) and this week I have only 2 booked so far.
You have to get out and talk to people and network. I've been so busy that I haven't had much time to do it, but am putting together packages now to hit up some fleets this week. You may get paid less for them but it's a way to get some regular business. At least that's how I look at it.
I know my business isn't going to just grow on it's own and I need to push it. I'm connecting with the right people and trying to get help from my friends and family whenever possible. You'd really be surprised at who your friends might know. For example one of my buddies has already brought me 2 decent accounts. Both personal owners but one has 7 cars plus the rest of his family, and the other about 20 cars. Plus a business with a fleet that I may be able to get in with.
Word of mouth and always ensuring your customers leave you happy is definitely huge. But also just getting your name out there. Weather it be by yard signs, vehicle decals, being on websites (facebook, twitter, etc). The more your name is on the internet too the better results you'll get when someone in your area does a google search for detailing.
Just some advice that I've found helpful so far.