Question

For a research paper, you have just compiled a stack of resources in your school library. Which aspect would be best to consider when determining each source’s validity?

Answer 1

Short answer, check the bibliography and publication dates.
Long answer, do the above and look for peer reviewed sources, evaluate the quality of research (if applicable), and look up citation lists (who else used this information and by which authors). When you see a pattern of reputable listings, consider expanding your sources using the citation lists. In the discussion, I usually address information/viewpoints I have chosen to not use and the reasons why; and use these factors to support my conclusion.
Don't wait until the last minute is another important aspect.