How should I study for the A-level exams?

The best thing to do is making your own notes and making sure that you understand the topics. And then, you can start doing past papers (without looking back to your notes), and see which topics in particular you are unfamiliar with. It will also help you to get an idea of what kind of questions will be asked in an exam. From that, focus on your weaknesses. After another revision, do the papers again until you feel confident in answering the questions.