Useful or Relevant.  Many databases include abstracts, which are very helpful in determining the value of each article in relation to your research project.

Timely.   The date of the articles will indicate the timeliness of the information, which for some subjects is very important.  Most databases arrange your results list in reverse chronological order, putting the most recent publications first.

Appropriate and Authoritative.  Another big question with articles is the difference between scholarly and popular periodicals, and when each is the appropriate type of source.  Sometimes you will be required by your professor to use scholarly publications.  For more informal subjects a popular news magazine might be good.