How do I study for my mid-term exams?

I'm now a freshman in high school and so far in my life have never really had the need to study. Well, now we're about to have midterms and, even though I know most of the material, I'm going to freak out if I don't study. Does anyone have any good tips? I usually can't study because I'm not used to it and find it incredibly boring. Tomorrow I have Geography and Geometry exams if that changes anything. Thanks in advance!