well my best tips for A level maths revision are as follows;
Try to maximise every past paper you do, by this I mean always try to do them in timed conditions, and most importantly, see where you are going wrong and analyse to find your weakest areas (also repeat questions you got wrong, unless it is only a trivial mistake i.e. signage error or losing an exponential)
Once you have found your weak areas, hit them hard with questions until they are your strongest areas, for me this was D.E's in C4.
Try to find relevant material which is slightly more challenging than official papers, if you are on edexcel the Madas maths C3/C4 papers are amazing (I think
@TeeEm produced these? If so, thank you). I really can't recommend them enough.
When it comes to the exams my tips are;
Become expert in timing papers, learn to eat up easy questions in as little time as possible and be sure to leave anything you don't make meaningful progress on quickly on your first pass of the paper, as the problem will stay on your mind as you work through the other questions and you will be able to focus more in a relaxed manner once you have almost completed the paper.
Don't be phased by questions that seem hard, as they
will be solvable using A level techniques you've learnt, sometimes it is just presented in a bit of a different way. Make sure you are one of the people who sees through the examiners tricks.
Believe in yourself! You are one of the better candidates sitting this exam and you will be successful. Trust yourself and the work you have put in, I have always felt that the revision stage is the stressful/difficult phase and the exam is a bit of a relief.