Here are some tips which I think helped me get the A* for my maths A-Level, and I hope they will be of some help to you as well. If you have any questions feel free to ask them in the comments section 😊
1. When doing past papers, leave the most recent 2-3 papers till last, and do the rest of the papers in reverse chronological order (since older questions are more likely to come up in your exams than the recent ones, but the most recent ones will prepare you for how hard your exam will likely be). You can keep track of the papers you have done by using a printable that I have made, which can be downloaded from here.
2. Write down the questions you found challenging or got wrong in past papers in a notebook, and write down how to reach the correct answers in there as well. You can use the notebook as a last minute revision tool just before the exam, and writing down the questions and answers in a notebook will prevent you from getting the same type of question wrong again if it turns up, as you will have gone through it twice.
3. If you have the time, try some solomon papers - these will be more challenging than the normal past papers and will prevent you from panicking if a harder question than normal turns up in the exam. You can find solomon papers along with any other exam papers which exist for A Level Maths on http://www.physicsandmathstutor.com/a-level-maths-papers/
4. PLEASE NOTE THIS ONLY APPLIES TO THE UNREFORMED EDEXCEL MATHS A LEVEL: Since the criteria for an A* for maths is to average over 90% for C3 and C4 and to average over 80% overall for the 6 modules, you should spend most of your time revising for C3 and C4 compared to your other modules. If you had to cut it really close, you could get an A* with just 75% in 4 of the modules as long as you got 90% or over in C3 and C4 - obviously this isn't recommended lol but it's just to prove a point that it's better to do very well in those 2 modules than to spend time trying to perfect your other ones if you're aiming for an A*.