Visit standard bestseller lists in newspapers like The New York Times, USA Today or Book Sense. These lists represent what is currently selling and how well the books stack up against each other. The methods used to determine bestsellers vary, and USA Today generates only one list, whereas The New York Times provides lists for different genres and formats, such as hardback, nonfiction and self-help.
Check major bookseller websites like Amazon, Barnes and Noble and Books-a-Million websites to see what their major sales are. These are usually available in weekly, monthly, daily or up-to-the-minute lists in nearly all different genres and niches. While the books on these lists may ebb and flow, they represent a good idea of what people are buying, as online sales are not noted in all major bestseller lists.
Check with chain bookstores and superstores that sell books, as they generally have a section with the week's bestsellers. These are usually either bestsellers in the country or at the stores nationwide.
Purchase a subscription to use Nielsen Book Scan, a comprehensive compilation of book sales and numbers, including different formats and editions. While use of this service is quite costly, it represents the most thorough and accurate data on bestselling books.