Currency: When was the book published? Currency varies with different disciplines. Check your assignment for requirements. Your assignment may require that books are published within the last five years.
Relevance: Who is the author? What are the author's credentials? Does the author have a Ph.D? Are other sources cited?
Authority: Who is the publisher? Is it self-published or published by a University Press?
Accuracy: Is the information presented in the book supported by evidence?
Purpose: Who is the intended audience? Is the author writing for information, opinion, or a memoir?