The words AND/OR/NOT (sometimes called Boolean) can be used to group sets of search terms together in a meaningful way; which will improve the quality of your search results because you are customizing the results to suit your specific needs/topic.
Search filters can be found in ArticlesPlus, other library databases, and even Google Scholar and are (usually) found on the left-hand side of the results page. These help to limit your results in a way you can control.
Have a specific phrase, treatment, test, etc. and the words have to stay together as they are in order to maintain the definition? Example: CPR stands for "Cardiopulmonary Resuscitation". Put quotation marks around the phrase "Cardiopulmonary Resuscitation" so the databases does not search for the words Cardiopulmonary and Resuscitation individually in attempt to get you more results.
An ArticlesPlus search for "Cardiopulmonary Resuscitation" gets less results than Cardiopulmonary Resuscitation
Want to get more results easily? Add the asterisk * to the end of a word that can have multiple endings that would be relevant to your search. For example: teen*. This will search for teenage, teenager, teen, teens and any other possible endings.