Do not wait until the last minute to start studying! It’s the worst when you try to cram all that information in the night before a big test. You’ll forget stuff when it comes down to test time, and you’ll be exhausted.
Instead, plan out studying ahead of time. If you have a syllabus, you should know when your tests will be. If not, most teachers give a few week’s notice before a test. If they don’t, then ask! Take the initiative to find out when you need to start preparing.