If your book is for kids, you might consider advertising your event (yes, it's an event, not just a booksigning) as a reading. Advertise to parents to bring along their children. Take five minutes and read part of your book. You'll hook the kids, who'll then beg their parents to buy the book for them.

Make sure you wear a nametag so that everyone knows you're the author.

Oh, and find out where the bathrooms are. You're gonna be asked.