No matter which type of source you use, there are general guidelines you should apply when evaluating them. Think about who, when, why, and what:
Who wrote it?
Knowing who wrote the information you are using can help you to determine if the information is reliable.
Is the author identified?
Is any information given about the author?
How does the author know anything about the subject?
Is the author affiliated with an organization or institution?
If you need more information about an author, ask a librarian to help you.
When was it written?
Knowing when the information was written may or may not be significant for your subject. For some subjects, you need current information; for others, older information is useful.
Is there a publication date?
Is the information up-to-date?
Why was it written?
Knowing the author's intent will help you to make an informed decision about whether to use, or how to use, the information.
Read the material to see if you can determine the author's motivation. Are they: