Look up the course description on the department's website. Before each registration period, departments post lists of courses, which sometimes include required textbooks. Sometimes, these books will change before the class begins. Always keep your receipts, and leave wrapped books unopened until the class has begun.
Check the campus bookstore or online booksellers, like Effolett.com, that have received a book list from the professor. About a month before the semester begins, the bookstore should have all the books on the shelf. The books should be filed under the code and number for the class. For instance, a first-year English course might have the code: "ENG-1100."
Review the course syllabus, which should have a list of required and suggested titles. If the class has not begun or if the syllabus has not been distributed, email the professor for a copy of the syllabus. Also, query the professor to find out if alternate editions of texts will work.