Use AND to combine two different ideas. AND narrows your results.
Examples:
"academic success" AND sleep
"time management" AND grades
"growth mind-set" AND transition AND college
tuition AND admissions AND "college attendance"
Use OR to combine similar concepts. OR expands your results.
Examples:
grades OR GPA
study OR learn
college OR university OR "higher education"
self-discipline OR self-control OR "self regulation"
discipline OR determination