Evaluating sources is important not just for academic research but in one's ability to make sound personal, financial, health, and professional decisions.
There are several facets to consider and many questions you can ask to help you evaluate a source. At its core though, this is about honing your ability to sense when someone (maliciously or unintentionally) is making fraudulent or poorly supported claims, twisting or obfuscating the truth, or just plain trying to sell something.
This may initially seem like a lot of questions to have to ask of every source, but over time it will become an almost unconscious force of habit and you will be able to cut through the glut of information more quickly.
Here are some of the things to take into consideration when evaluating any source of information:
1. Author Credibility
What are the authors credentials/qualifications? Is the author a scholar, expert, journalist, etc.? Is the author cited and an authority in the field? A scholar may be outside the mainstream of thought in their discipline (this doesn't necessarily mean they are wrong or right). But, it does need to be taken into account and understood in relationship to the broader consensus. Is the author clearly identified? If not who is the authoring body and what is their purpose? Is the author writing in a professional capacity (in an academic journal) or are they writing on a blog or editorial section?
Authority and established credibility are both standard criteria to look for when evaluating sources. Ultimately, though it is the quality of evidence a source uses to substantiate their claim that is of utmost significance. Do they clearly cite their sources? Can you verify the accuracy of their evidence? Does the source engage with other research and scholarship on the subject? Does the author posit claims which are unsupported?
Is the author affiliated with any special interests? Does the author advocate for an groups or ideological views? Is there a funding source which might present a conflict of interest for the author? What evidence does the author use, do they address opposing arguments?
4. Purpose, Audience, & Argument
Who is the author writing for? Is the source providing information, commentary, selling something? Are there advertisements? What is the author's claim? Is their evidence sound and verifiable? Do they employ logical fallacies? How does their interpretation compare to others?
Does your research require up-to-date information? When was it published or last updated? Are they citing obsolete or since-corrected information? For books, is it the latest edition or has it been revised? Do all the links work on a site? Broken links can be an indication that the site is not being administered or is out-of-date.