Note making:
Make notes (hand written) according to the syllabus dot points as you work through the syllabus: from text books, study guides and note taking stuff the teacher says in class. I wouldn't recommend using other people's notes for your own study because it won't benefit you in the long run; you understand the content better when you write your own. But to make sure you're on the right track, you can look through the notes of others and write stuff from their notes onto yours if you haven't covered it.
Exam prep:
For English, know your texts really well (memorise quotes and language techniques etc.) and practice writing essays in exam conditions ie. 40 minutes
Also, practice composing your own questions and try not to memorise essays because the question may not cover your essay topic; you need to learn how to spontaneously adapt yourself to questions you haven't been exposed to before.
Just know your texts really well.
Maths and sciences:
Practice questions and past papers. Continuous practice is essential.
Study:
Revise your work everyday or frequently to ensure that the content is permanently embedded in your head.
Don't study hardcore - study for however long you can remember and understand the content because that is all that matters.
Remember not to overwork yourself and take frequent breaks to remain motivated. So perhaps, 3-5 hours study a day?
When studying, focus more on your weaknesses rather than your strengths so you can gain extra marks.
Study methods differ for each person, but I find rote learning, writing and oral speaking information to be most effective.
You can try visual methods like graphs and diagrams so the concept is easier to understand.
Oh, and do past practice papers so you can become adapted to the exam setting and style: you can ask your teacher, get some on bored of studies or the internet.
Good luck!