Look for the following information about your source. You may not always find everything, but these are key points to consider. If you cannot find this information about your source, then it may not be a good source to use.
Who is this author? What do you know about their credentials? Why are they a reliable source of information on this topic? Are they an expert in this subject? Do they have an advanced degree from a university? Do they have lots of experience in this subject? To learn more about your author, Google their name. You might find their LinkedIn page, resume, university profile or personal webpage. Ask a librarian if you need help researching an author.
Publisher or Sponsor
Examine the publisher of the book, periodicals or website. What do you know about them? Have you heard of them? Are they reputable? Well-known in this field? Biased on the topic? (Hint: you can ask a librarian or your instructor about the publisher's reputation if you're not sure.)
How biased is this source? Look at the author and the publisher - are they associated with a company, organization, institution, agency, etc. that would make them biased on this topic? Are they only telling you one side of the argument? Are they giving objective facts or opinion? Where are they getting their information from (what are their sources)? Are their sources biased? (Hint: pretty much everything is biased, and it's possible you can still use a biased source as long as it isn't too biased, and you can take the bias into account when using the information in your paper. Maybe look for other sources that present a different viewpoint to counteract the bias).
Where is the author of this article getting their information? Do they cite sources at the end? Or do they refer to sources they used throughout the text? Do their sources look reliable/official or biased or not authoritative? If the author cites no sources, are they relying on their own expertise or first-hand experience (refer back to author's qualifications)?
Look at the date of the source. How current is it? And how much does currency matter? Some subjects need to be more current than others (i.e. current events and technology go out of date very quickly, health information is only good for five years or so usually, but something historical would be useful much longer).
Who is the audience this source is geared to? Is it children, students, the general public, experts in a field, scholars and academics? Obviously, something geared for children is not appropriate for you to use, and something geared towards the general public may be okay depending on your purposes, but a scholarly source might be more detailed.