When studying your topic/unit materials and notes, the items you should specifically highlight are the really important details, important phrases, key terms, and important names. If it were me, I would just highlight everything that I know will help me memorize the other details, and then read those parts over and over again, until I can literally see the words and sentences seared into my eyelids. It is best to use this method right before the test, if you have free time you can use to study. Warning! I never said that this could be easy, so don't just trust my answer, because each person has a different way of studying and this method probably doesn't suit you. If this doesn't, then I am really sorry, but it's better than failing a test or something.
I hope you like this answer, and have a good night! :)