We decided on our preschool by location, curriculum, teacher experience and overall feel of the place. I have a daughter in preschool now and what I look for is communication, communication, communication. Since her answer is "nothing" when I ask her what she did for the 2 1/2 hours she was in school, it's up to the teacher to help fill in the gaps.
I think in this economy, pricing is key. I think a lot of families are skipping preschool beause it is optional and a real expense. I think if you price your school at the bottom of the scale, but still provide excellent teachers parents will seriously consider your school. Plus, I think you have to advertise in some way. We went looking for preschools without having any idea which schools were in the area - if one had reached out in someway I may have given them preference.