Visit Goodreads.com. This is a site dedicated to cataloging books. You can search for the book you want to learn about by title, author or International Standard Book Number (ISBN). In the results, you will be presented with a list of all possible matches, and all of the various editions of each book are included in the list. Depending on how rare or common the book is, the information available about it may include a biography of the author, publication history, and other facts as they are available.
Visit a reputable used book store. The proprietors of these stores make it their business to be knowledgeable about their products. If they are not familiar with the book you are researching, they will likely have catalogs and other industry publications in which to look it up. Depending on the type of book you are researching, there may even be a store that specializes in that genre. The Book Stores Guide can help you locate a shop in your area.
Ask your librarian. The people working in your local library are likely to have master's degrees in library science. This arms them with the knowledge necessary to navigate the various channels available for researching books. If the book is not one available in the library itself, chances are still good that the librarian can find whatever information there is available about it.
Contact the Library of Congress. If you are researching the value of an old book or books, the Library of Congress has materials available that will aid you in that effort. By writing to them, you can obtain the latest copy of the Antiquarian Booksellers' Association of America's annual directory and a copy of Your Old Books, which is a pamphlet-style guide to researching book values.