I often have a hard time offering advice to students about how to study more effectively. And countless students tell me that they studied "really hard" for the exam, but still performed poorly.
Re-reading over Powerpoints (rather than taking their own notes) is one major culprit. Failure to work any problems, or to learn from working problems (i.e., not just immediately looking up the answer when they don't know) are additional culprits.
According to the article linked below:
"the majority of students study by re-reading notes and textbooks — but the psychologists' research, both in lab experiments and of actual students in classes, shows this is a terrible way to learn material."
Read more here.