You've gotten some great responses. I wanted to add:
It takes 5-7 times for someone to see your sign or ad before they usually respond. So, you have to put yourself every where!
Where do the mom's that need daycare work? live? shop? exercise? get their hair done?
Where do mom's with kids take their kids? dance? tutoring? karate? sports?
Make a nice flyer (make sure it is proofread!)and business cards, dress professionally and hit the beat! Introduce yourself to every manager in all the local restuarants, stores, boutiques, etc. and leave your card and flyer. If they have a bulletin board, ASK to post your info. Make a thirty second introduction that says who you are, the name of your day care and they fact that you are providing licensed day care in a loving home. Then say that "if you are not looking for a day care provider, maybe you know someone who is. Can I leave my information for you or anyone else here that may need it?"
While you are out, you will want to hit all public service places: libraries, YMCA's, churches, hospitals, clinics,etc. Some have bulletin boards!
There are web sites that allow you to post your day care. One is www.care.com It is free if you do not pay them to run a background check (which you already have).
When placing a craigslist ad, do not give out too much information. Make it professional and to the point. You do not need the crazies! If you have a web site of your own (I highly recommend that you get one), then just post it in your ad on craigslist with the basic information. You may also want to include a call window.
Lastly, I hope you have a contract that includes just about anything and everything that could go beyond what you would expect normal. There are a lot of different people out there who have their own ideas of what normal is.
GOOD LUCK!