Here are a few things to look for and keep in mind. I will give you some examples of things I really liked about my daughter's preschool...not in any order.
Communications with staff and ability to work with you-the director of my daughter's school quickly replied to my emails with questions concerning the school and asking for a tour. Even now she replies to emails in a short amount of time, even on the weekends and after hours
Cleanliness-her school was and has always been very clean. I was impressed when I toured. The kids were also very clean....faces and hands weren't grimy and there were no snotty noses. In fact, as a rule the kids have to wash their hands as soon as they enter the classroom. As a result, the kids are never sick. My daughter has missed one day of school and that is because the had an ear infection.
Politeness-when I toured everyone was so polite, welcoming and friendly to me and my daughter. Even the kids in class were extremely nice and well behaved. They invited her to sit and have snack with them.
The school is play based meaning everything the kids learn is through playing.
They are okay if a child is not potty trained....in any grade (although the kids that had been in the school since they were two were potty trained by the time they were in the 3's class) They work with them on potty training
Discipline-they only notify the parents if it is a huge issue and it is something they have been trying to stop but to no avail. Otherwise, their first choice is redirection. If that doesn't work then they get rewards and consequences....that has happened one time the whole time my daughter has been there since August. One time one of the girls started screaming at the top of her lungs and of course that started a chain reaction. The teachers couldn't get anybody to stop so the rewards and consequences began. If they wouldn't stop they would have to sit in time out for a few minutes. However, if nobody screamed then they would get a sticker or bubbles as a reward.
Snacks are relatively healthy....not every meal but they try hard.
The playground is so important. We have some schools here where the playgrounds are on concrete next to a busy street...that doesn't sound like fun! Others are in full sun. I love my daughter's school's playground. Her school is downtown but the playground is facing a nice quiet street. The ground is sand. There is a huge old oak tree covering half of the playground. The play equipment is low to the ground. A lot of the items on the playground require imagination. If it is too cold or wet to play outside, then they play in the gym that has several bicycles, scooters, balls, and playhouse with a slide.
There are large windows looking into each classroom and parents aare welcome to come by anytime. They do lock the doors to the hallway to the classroom as a safety issue,...if one child some how escapes they can't get out of the building (you would be surprised at how many stories I hear about kids just wondering around--from other schools of course!).
Teacher turn over rate is extremely low. I think most of the teachers have been there for at least 15 years. If one teacher does leave it is usually because their husband has found a job elsewhere.
It is not NAEYC accredited (I believe it is really expensive to get accredited) but they follow all the guidelines. **Edit** Just for fun I thought I would do a search on NAEYC accredited schools in my area....the closest are 25 miles away in other cities.
Okay, this was a long post. I hope it helps give you some ideas to look for or ask about.