If you can, visit some more at the school - maybe a picnic on the playground (now during the summer)?
Send the teacher a drawing your child did for him/her - maybe they will send a reply back? I know of a preschool teacher who had a tea party with a child who was reluctant to switch to a new school this year.
See if you can get a few phone numbers of classmates and have some playdates with those kids (one on one, at your house and then at theirs) so your child has some friends in class on the first day.
Let the child pick out a "first day of school" outfit, backpack, etc. Put the child's favorite teddy bear or what have you in the backpack. Just knowing it is there is often a big comfort.
Choose a school with a very warm, loving teacher. This was my top criteria when choosing a preschool.
And the biggest thing (IMO) that you can do is to have a positive attitude yourself. I personally loved school and just glow with excitement when I talk about it (mine or my kids') - they followed suit. On that first day, my husband left for work late so he could be there that morning to help and be there on that big day. I took tons of photos - of the child getting ready, all dressed to go on the front porch, at school in front of the sign and with the teacher, etc.