Use a planner. I always write ‘TEST DAY’ on the actual day of the test in my planner, and it also helps to use a color-coding method (red for due tomorrow, yellow for in a few days, green for a few weeks away.)
Create a “study plan”. In your notebook write down when your tests are, what material they are on, and how long you want to study per day. I usually study for most classes 20 minutes a day, starting 3 days before a test.
Use different sources. I have found that it isn’t very useful to just read a textbook over and over again, you could use other materials such as online flashcards, mnemonic devices, and video and audio resources. Crash Course is a very good resource, and I also use a online site called Quizlet which can be used on the go!
Put the information in your own words. Many textbooks and teachers use big words, so an easier way to understand it is to put it into shorter, commonsense words that are easier to remember.
Go to a museum, visit a historical site, etc. If you see something in person, it is easier to ‘connect the dots’ and be able to understand the material better than you would just reading your notes.