1.) Figure out if the source fits your specific needs. As students, you need your sources to:
This means that sometimes a blog post will be the best source, and sometimes a peer-reviewed scholarly paper. The type of source depends on the type of research you are doing, and your syllabus is a clue as to what kinds of sources will work.
2.) Figure out if the source is credible. Credibility is a hard concept to define, but it essentially means a source that a person conversant in the field would be able to reasonably trust as having legitimate information or being produced via proven methodology. As students starting out, you aren't expected to instantly know what sources are good. There are a couple of basic concepts to keep in mind:
Scholarly sources usually refer to sources created by scholars in a scholarly manner. Typically, this means that the article or book has gone through some variation of Peer Review and/or editing, in order to catch mistakes. It also assumes that the author has relevant expertise in the field they are writing in.
Figuring out if something is scholarly can be tricky, but there are a couple of rules that you can keep in mind:
There's no one easy way to figure this out, but keeping these general guidelines in mind can help. Many databases in the library also have an option to select only Scholarly or Peer-Reviewed items, so that is an excellent short cut.
This video also provides a distinction between scholarly and popular sources.