When choosing keywords for your topic, you'll want to consider the major concepts addressed by your research question(s) and come up with a list of synonyms or related terms. For example:
If your research question is: What is the connection between smoking and depression among teenagers?
Major concepts for this topic might include:
Synonyms or related terms might include:
When doing a keyword search it's a good idea to try a number of different search terms and phrases. Don't be discouraged if your initial keyword search brings back too many, too few, or irrelevant results--you'll want to try multiple keywords, synonyms for your keywords, different combinations of keywords, etc. to bring back the best results. Check these videos for more help choosing and using keywords: