Dd is 1 but I've been looking around for when it's time to start. My mom is becoming a preschool teacher. We all helped my sister hunt around for the right one for her preschooler. We look for a learn through play program that actually communicates with parents. My mom worked at one and they were horrible to the parents! Also if you want it to be religiously affiliated or not. I wouldn't put my kid in a preschool that was religious in a way that I didn't agree with.
My sister witnessed a child being spanked and was fired for telling the parents so I always recommend making sure LO understands to come to you if they are hurt or feel threatened.
I asked about what they would be teaching, how they discipline, what foods were served and how updated they would keep me on how he was doing.