There’s truth in the “practice makes perfect” theory. Depending on what you’re studying for, make quizzes for yourself. Whether it’s vocab, science or math, you should test yourself beforehand to get ready.
Ask your teacher for the types of questions (multiple choice, fill-in-the-blank) that will be on the test. That way you can make yourself a quiz that will mimic the test and you won’t feel surprised come test time.