Assign them to read something by the author, or have the school librarian or the teachers read the author's books to the students. Some schools buy paperback copies of the authors books and give one to each of the students. Give students some fun assignments that relate to the concepts illustrated by the author's books. Plan the author visit for a time when writing is a major curriculum focus, for example, during a Young Authors fair, or during preparations for a school writing contest. Invite parents in for the author presentation.
Parents frequently get as much from the author visits as their children.
Prepare the students for the presentation. Give them some things to look for. If you don't want to bother with ordering books, a local bookstore will usually be glad to handle the booksales for you. Or if you need a fundraiser, you can order the books wholesale, sell them retail, and keep the profit. Or you can pass the wholesale savings on to the students.