First and foremost, good job for taking the initative to start improving your grades - it might feel late, but most Year 11's don't start until the last three months.
The most important thing for revision are concepts called active recall and spaced repitition. You'll see these brought up a lot when it comes to study videos and such on youtube, but in essence they're scientifically proven as methods to ensure our brain commits concepts to our long-term memory. You'll need to remember things like qoutes from your texts and poems for English Literature as well as statistics and figures for history and such, so the best thing you can do is find a method that incorporates these two things which works for you. The one I advise most is flashcards, but make sure they're engaging. Use a software like Quizlet or Anki to make flashcards which make you actively think about the answer to a question before you see it -- do not passively read notes.
For things like triple science, you're already on the right lines, but what makes the difference between a grade 6/7 and a grade 8/9 is your ability to pick up those silly marks and do well in application questions. Application questions are those questions where you've literally never been told about the concept, but have to apply your existing knowledge to a new concept. The best way to do this is to make sure you understand concepts by learning them thoroughly - don't memorise, understand; use videos, ask your teachers, go to tutoring sessions, etc - even teach your friends! If you can teach a concept at a level where a five year old could understand it, you know it.
Make sure you're keeping ontop of things; your learning isn't done yet. Things like the Space unit on Triple AQA Physics and Magnetism are difficult, but you can get a 9 if you learn them properly.
Best of luck - work hard.