Mrs. B. told me that the young adult books are really more appropriate for 9th graders and below; upperclassmen tend to prefer a wide range of popular books written for adults. Along with "fluff" books like Sweet Valley High, students tend to enjoy authors like John Grisham and James Patterson. They also enjoy reading the Oprah Book Club selections; however, Mrs. B. pointed out that Oprah has recently begun focusing on classics like Anna Karenina which tend not to be as appealing to students because of the length.
Another indicator of popularity is whether a book has been made into a movie. The Lord of the Rings and Harry Potter books are extremely popular for this reason.
When ordering books, Mrs. B. primarily consults the School Library Journal. She reads the book reviews and also browses the bookstores to see what they are carrying. She also consults the LMC and Booklist. She doesn't have a lot of room to create special displays to feature particular books, but the students seem to have no trouble finding what interests them. Also, many of the "fluff" paperbacks that are so popular for light reading sit on a carousel near the front of the library.
In her quest to stock books that will interest students, she uses movie tie-ins when possible and tries to take into account the students' preferences according to the circulation patterns. She also has a stack of book-order requests on a little table in the library. Students fill out these requests frequently and she buys the requested books whenever possible. Students have commented in surprise that she actually pays attention to their requests. Her response is that she'll do whatever it takes to get them reading and interested in books.
* I am using her initials until I obtain her permission to publish her name on the internet.