The single most important thing you can do is build your vocabulary. You can understand all the history in the world but if you can't understand what a question is asking you it's exponentially more difficult. And recognition (seeing the correct answer/recognizing the correct answer) is much easier than recall. Recall means YOU build the answer. For example, recognition is selecting the right answer on a multiple choice Recall is writing the correct answer yourself. Or, as I like to say, it's the difference between what you think you know and what you actually know.
On the Quizlet site there are word banks organized by theme. They are paired with the FreshPrep songs available on this website. I highly suggest downloading the free Quizlet app and reviewing the relevant vocabulary daily. You will be required to turn in vocabulary sets in class as well as part of your grade.