Work smart. A recurring answer when we laureates are asked to give tips is: work as hard as you can and then even harder. However, it might not be necessarily the best thing to do. During L6 and U6, we are flooded with homework from both school and tuitions. Most of these homeworks are identical or very similar to each other. Personally, I found it a waste of time to do the same things over and over again. Sure, for concepts that were difficult to grasp, repetition does help. Instead, find alternative practice questions to do, or simply rest!
Relating to my previous answer, REST is essential. It is certainly even more important as you are nearing exams. In my opinion, there isn't much difference in terms of knowledge and skills between you and other toppers in your year. What makes the difference during exam time is how well you feel. (things contributing to that are: good physical and mental health and rest) You certainly don't want to experience burn-out.
A healthy attitude towards exams is required. All you can do is try your best really. Work to better yourself everyday and not to surpass others. Don't expect to be a laureate; instead look at all your options, make plans if things do not work out. This will significantly reduce your stress levels and allow you to work more efficiently.
Identify and own up to your shortcomings. All my life, i have struggled with languages. To this day, I still cannot speak french fluently! When choosing my AS subject, i went for Biology instead of french even if people told me french is light work and easier. Don't listen to them, you know yourself best! On my first attempt, i came 10th on girls' side and I believe the reason is because of GP. Knowing that i am not great at GP, and that it could still fail me at my second attempt, my strategy was to improve my main subjects (which i loved and enjoy working at it) as much as i could, to compensate for it. Of course, i tried improving my GP as well but I never felt like i actually did.
Even if the above tips do not seem like proper advice, for me individually it made the most difference! Okay now for a concrete tip, i would advise you to broaden your range of practice papers. For Maths, i found the Ah Teck book interesting and for chemistry i practised OCR and AQA papers. I am a visual learner and i found learning on youtube quite useful as well.
After you finish your paper, cross-check your answers by plugging them into the questions and see if they fit in. You can't do that for all questions however, but it still reduces the time taken to cross-check some questions.
Work out other papers such as AQA and OCR. These are similar to Cambridge papers.
Do not be afraid to go beyond the number of lines given if you feel like your answer is not complete and you can still enhance it.
Being concise is better, however, because it saves you time.
Do your practicals properly and get as familiar as you can to different set-ups.
Use reports as well as marking schemes when you are self-marking your papers.
Only God can help us!