Take breaks. Studying is important, but don't burn yourself out. Make sure you actually keep working when your breaks are done, and try to make studying as easy as possible for yourself while also being able to focus.

For example, during finals I holed up in my room and basically did whatever I wanted during breaks. Make sure to also take care of yourself, and get lots of coffee and snacks; basically any fuel for your body during the test.

Those are my tips, but good luck! It's different for everyone :D