There is 2 main things you need to get an A* and will differentiate you from everyone else.
The 2 things are understanding and practise
You must truly understand what is going on and be able to explain it to someone else, at A-levels they will be testing your understanding by taking key concepts and giving it to you in unknown scenarios. To insure you have understood something try teaching it to someone else and see if they understand it.
Read your notes then get a scrap piece of paper and spiderweb all the information you have understood and link it to other topics, as subjects tend to be very much interlinked.
You may have understood the topic but you may not be necessary able to apply this knowledge in exams. This is where past papers come in handy, this allows you to practice the skill of applying knowledge. It is all good and well understanding topics but if you can't apply it there is no point.
This is a short blogpost but these 2 steps are very important. Thank you for reading!