Look for the copyright date in the front pages of the book. While some topics never go out of date, many non-fiction topics become dated. For example, biographies may not cover newly discovered documentation, and how-to books may demonstrate older ways of doing tasks that are now simpler. Literary citation guides are an example; writers and scholars no longer use footnotes. They use in-text parenthetical citations and end notes instead.
Turn to the bibliography to evaluate the sources the author used. Also, scan endnotes if there are any. Later, as you read the main text, you will find it easier to locate the additional information they offer. Having scanned them will also heighten your awareness that there is more information.
Read the foreword, introduction and preface if they are available. They often offer valuable information that will inform your reading.
Take notes on the highlights of the book and on the parts that particularly interest you or that you question. This is helpful if you plan to write a paper on the book or if you will have to sit for an exam on it. If it's not a library book, taking notes right on the pages will save you a great deal of time and will less likely disrupt your reading. Also, if you sit for an open-book exam, the notes will help you during the exam.
Evaluate what the author says in the light of common sense, history, your background knowledge and other reading you have done. Maintain a mind that is open to new ideas and ways of looking at the subject but one that is skeptical enough to look for support and solid reasoning. Support refers to expert studies, statistics from credible sources and the ideas of trusted experts and scholars.