Example:
Articulate the subject you want to investigate:
Is academic performance impacted for commuter students?
Identify the words/phrases that constitute the main topics:
Is academic performance impacted for commuter students?
Start searching using your own vocabulary for your topics
Review some of the full records on the result list and look for subject terms used in ProQuest PowerSearch that are synonymous with your search terms
Redo your search combining your terms and all the database subject terms you found:
"academic performance" or "academic achievement" or "grade point average"
AND
"commuter students" or "commuting students"