When evaluating sources consider:
Authority: Who is the author and publisher? What are their credentials?
Purpose: What is the intent of the author, editor, or publisher? Sometimes the introduction, preface, or back cover give hints at this!
Objectivity: What is the bias? How objective or subjective is the work?
Accuracy: How credible is this source? Corroborate the information or arguments of the resource with other sources.
Currency: When was the work published? Is it relevant?