Evaluating the authority, usefulness, and reliability of the information you find is a crucial step in the process of library research. The questions you ask about books, periodical articles, multimedia titles, or Web pages are similar whether you're looking at a citation to the item, a physical item in hand, or an electronic version on a computer.
Critically Analyzing Information Sources lists some of the questions you should ask when you consider the appropriateness of a particular book, article, media resource, or Web site for your research.
Use book reviews to gather critical information about books. Three quick ways to access them online [Cornell users only]:
More sources for book reviews --> Book Reviews: A Finding Guide.
Distinguishing Scholarly from Other Periodicals shows how to evaluate periodicals by looking at their format, intended audience, and appearance.
Evaluating Web Pages: Questions to Ask & Strategies for Getting the Answers is an excellent guide from UC Berkeley.