Not all resources are created equal! There are a number of criteria to consider when determining whether or not a source is reliable (able to be trusted) and appropriate for your academic work.
Who is the author?
What makes the author an expert in the field he or she is writing about? What are his or her qualifications? Does he or she have education or work experience in the field? Has he or she published anything else about the subject? (HINT: Google the name of the author to find this information).
If there isn't an author listed, is the information authored by a government, corporate, or non-profit agency? Is the agency or organization recognized in the field in which you are studying, and is it suitable to address your topic?
Point of View or Bias
Does the source promote one point of view or one agenda?
Is the information provided as fact or opinion?
If the information is found online, does the Web site have advertisements? If so, are the ads part of or separate from the rest of the site?
Does your topic require current information?
Does the source include a date of publication or a "last updated" date?
References to Other Sources
Does the source include a bibliography or links to other web sites?
What types of sources are cited (primary/secondary, popular/scholarly, current/historical, etc.)
Relevance to Topic and Assignment
Is the information you found related to and useful for your topic and assignment?
Is the source the appropriate type for your needs? For example, do you need a book or a scholarly journal article? Do you need primary or secondary sources of information?