When looking at any new source of information (books, articles, websites, etc...) you should carefully evaluate it in terms of some basic criteria:
Information can quickly become obsolete. Supporting your thesis statement with facts that have been superseded by new research or recent events weakens your argument. Of course, not all assignments require the most current information; older materials can provide an historical or comprehensive understanding of your topic.
How do you know if the timeliness of your information is appropriate?
Relevance is important because you are expected to support your ideas with pertinent information. A source detailing Einstein's marriage and family life would not be germane to his theories in physics.
How do you know if your source is relevant?
Authority is important in judging the credibility of the author's assertions. In a trial regarding DNA evidence, a jury gives far more authority to what a genetics specialist has to say compared to someone off the street.
How do you know if an author is an authority on your topic?
Accuracy is important because errors and untruths distort a line of reasoning. When you present inaccurate information, you undermine your own credibility.
How do you know if your source is accurate?
Purpose is important because books, articles, and Web pages exist to educate, entertain, or sell a product or point of view. Some sources may be frivolous or commercial in nature, providing inadequate, false, or biased information. Other sources are more ambiguous concerning their partiality. Varied points of view can be valid, as long as they are based upon good reasoning and careful use of evidence.
How do you determine the purpose of your source?