Start by focusing on topics you struggle with. Read one page of notes. Without looking, make a mind map of what you remember about that page. Check and fill in with a different colour what you forgot. Turn what you forget into a flash card (online so on Quizlet or Brainscape/ or on a real paper card) Repeat and do this for the topics you need to learn. Do the flash cards at the end of each main study session.
Honestly this is one of the best revision strategies coming from a sixth former. Past paper questions help but you don’t have to worry about that at your age. Good luck and happy revising! Remember year 8 is all about learning how you learn and revise best, the grades and percentages are not worth stressing over even if they may seem really important at this age. Just try your best.