I started in the same boat as you. I have a full time job, only doing detailing and other things on nights and weekends. I am now to the point where I have just formed an LLC, gotten my EIN, and I am starting to set up all of my business related accounts so I can attempt to go full time within the next 6 months. I also have the standard facebook page and I just started my website. I don't just do detailing, I have also been doing a lot of custom work on headlights(projector retrofits, custom paint, etc). That is besides the point, though....
There are four things you need to do right now.
1. Write a business plan. How do you want to operate your business? How do you want it to grow? How much money do you want/need to make and what will it take to make that? Where will you conduct your business? These are all questions you need to ask yourself and have answers for. Having a written business plan will give you a guide in building your business.
2. Read the forums. There is a lot of great information and experiences on this site. I have learned a lot simply by reading threads and even watching videos on youtube. You can ask questions, too. These people are always willing to lend their expertise and it is a great thing.
3. Invest in good tools and chemicals. The detail is only as good as the product. You want to make a good name for yourself(or at least I hope you do), so spend a little more money now and get the things that will set you apart from the car wash downtown. You customers will appreciate it and the referrals will show that appreciation. You never know how many cars or friends your client has.
4. Marketing. Get your name out. Talk to everyone. Friends, family, complete strangers.....everyone. There is a good thread here about marketing strategies. The more you market, the better your business will be.
5. Practice and Train. Practice makes perfect. Practice on your car. Pick up decent body parts from junk yards and practice on them. Trying techniques before you need to use them will save you in the long run. Seek training...there is plenty out there. Nothing is more beneficial than having a pro tell you what to do and then watching you do it.
I threw in an extra step, and I am sure there are things that I am missing. These are just some of the fundamentals I have learned over the past year while trying to get things in order.