Be consistent and be regular in your revision since lower 6. Revise for any small school assessments (many students don't), you will memorise the topics better and this helps during your final revisions.
Practise as many past papers as you can. Try doing them within the time limit (at first it won't be easy) and note any mistake in a separate copybook. Do not forget to go over them during your revision. Clear all your doubts about anything however small they may seem.
Manage your time smartly. Allocate equal time for all your subjects. Try stick to a reasonable revision time table.
Do not worry about unnecessary things such as trying to compete with your friends, or you're not obtaining full marks. Be focused only on your studies. Give your best so that later there are no regrets.
Work in groups at school. Help each other and try motivating each other.
Practise many past papers. Correct them using the marking scheme.
Do your practicals properly in school or tuition. Be specific in your observations. Practise many MCQs, they are the trickiest. Keep the organic chemistry notes handy and go over them regularly. Follow the Cambridge syllabus guidelines properly.
Understand the concepts properly. Practise the old MCQs and questions, they tend to repeat. Follow the Cambridge syllabus guidelines properly.
Try writing an essay every week within the time limit (at first it could be hard). Do a detailed plan before writing. Practise paper2 comprehensions, read the MCQs properly, they are the trickiest. Stick to the number of words for the other questions and be concise.
Treat it as a main and allocate equal time for it. Use the Cambridge textbook and Follow the Cambridge syllabus guidelines properly.