Spread your learning sessions over time, repeat regularly. By continuously training your brain to retrieve information from your long-term memory, you strengthen the connections between the neurons in your brain, making it easier to retrieve information from your long-term memory (see forgetting curve). You can do this by, for example, creating practice questions (test questions, quiz questions) from the learning material of the past weeks (see retrieval practice). By alternating topics and types of practice questions about them (see interleaving), the learning material will stick even better. It also makes little sense to study for long periods at a time: your memory can only handle a limited amount of information in a row. If you try to learn more than that, things will also be forgotten again. It is comparable to the storage of your phone that gets full and where space needs to be made (see Cognitive Load Theory). Additionally, you quickly forget new information again. By regularly learning and repeating in short sessions, spread over several days, you forget the learning material less quickly. To do this well, it is important to make a clear plan: plan your learning and, if necessary, ask for help from your teacher or parents.
Dunlosky, J., Rawson, K. A., Marsh, E. J., Nathan, M. J., & Willingham, D. T. (2013). Improving students’ learning with effective learning techniques: Promising directions from cognitive and educational psychology.  Psychological Science in the Public Interest, 14(1), 4-58.
Roediger, H. L., & Pyc, M. A. (2012). Inexpensive techniques to improve education: Applying cognitive psychology to enhance educational practice. Journal of Applied Research in Memory and Cognition, 1(4), 242-248.
Benjamin, A. S., & Tullis, J. (2010). What makes distributed practice effective? Cognitive Psychology, 61, 228-247.