Consider what kind of resources you need. This will depend on:
See also "Fact check your news".
Make sure you know the date of the publication. Current information may be required for some assignments, especially in certain subject areas (such as political science or physics). For other assignments (such as history or literature) you may not need the most recent information. In some cases you might have been assigned to find older publications.
For web sites, look for posting or revision dates. Many dead links may indicate that the site is not up-to-date.
Who wrote it?
If you've been asked to find research articles, you will probably want materials written by professors, research scientists, or other experts in the field. Magazine and news articles are usually written by journalists who have investigated the subject but are not specialists.
Who published it?
Scholarly books are usually published by university presses (University of Texas Press, Harvard University Press) or by well-known commercial publishers like Routledge. Scholarly articles are usually published in journals from the type of publishers mentioned above and by scholarly associations.
A bibliography of the resources that the author consulted will be included in scholarly publications. Other publications may not include sources or may mention them briefly as part of the text.
Whether the author examined a literary text, ran scientific experiments, or conducted interviews with school children, the methodology used should be explained in scholarly articles.
Bias can be difficult to detect. If a publication comes from a source that you think might be biased (even if you agree with the bias) you might choose not to use the source, or to make clear in your paper that the source expresses a particular opinion.
About Web Sites
Internet resources often do not include information on author, currency, sources, etc. You may get clues from the publishing agency (is it an association? a non-profit? a govenment agency?). Also, the domain (edu, com, net, gov) will give you a hint as to the type of site you've found.