Hello!
Here are some tips:
• Get a good night's sleep. Believe me, if I don't get at least 7 hours of sleep before a big test, my mind won't function properly and I'll forget everything I'd practised. So, please, get enough sleep.
• Eat something good before the test. It'll help you. When your belly is full, almost everything is okay! :D Seriously, eat enough so that you wouldn't get hungry during the test, and you'll have less to think about. Also, make sure the food doesn't contain too much sugar.
• Take breaks when you're studying. Do NOT cram all those facts in your head, because they won't stay there. Set up a schedule and designate a specific part of every day to studying, and it shouldn't be longer than half an hour.
• Here's a bonus tip I've learned from past experiences. Please don't use TVs, phones, and anything that will distract you. If you need a calculator, USE A CALCULATOR, and not an online one. Otherwise you won't be as productive and it'll definitely distract you.