A large proportion of the marks in your Physics exam will be assessing your Maths skills, so a portion of your revision should be spent mastering skills like rearranging algebraic expressions and substituting values into them. Additionally, being comfortable converting units is a skill you should be well-practised in before sitting your exam. Maths skills aside, it's really important that you have a good understanding of the concepts covered by your exam boards. This doesn't mean just knowing definitions (though that is important), but being able to explain why something happens. Some students find creating flashcards helpful, others prefer to write notes out in their own words. Generally, going through notes with a highlighter is not the most effective technique for revision, make sure you are actively engaging with the content. Testing yourself is a great method of revising, so as you get nearer your exams, ensure you are answering as many exam-style questions and being strict with yourself when marking your answers. Finally, remember to take breaks, get fresh air and sleep well - your brain will take in information much better this way!
Most exam boards have a higher, or extended, paper - you will have to take this to access the highest grades. While you need to get the fundamentals right, like definitions, units and equations, the questions separating 7s from 9s involve applying knowledge to new contexts, describing experiments and interpreting data you haven't seen before. The best way to improve at these is through practice, so make sure you are trying lots of difficult exam-style questions before your exams. Don't be discouraged if you fail at these, they are meant to be challenging! Keep practising and learning from the questions and you'll be much more likely to hit those top grades.
The number of topics in your GCSE Physics course depends on the exam board you are sitting your exams with. That being said, most exam boards cover the same basic concepts of physics. These include motion and forces, energy, the particle model of matter, atomic structure and nuclear physics, electricity and circuits, magnetism, waves and sometimes space physics. If you are unsure, ask your teacher which exam board you will be taking - they will be able to provide you with a list of the different topics you will be learning over the course of your GCSE.
This percentage varies from exam board to exam board, but a good rule of thumb is that about 30% of your paper involves maths. Some of this will be calculation questions, but this may also include proportionality relationships (as one quantity changes, how the other is affected), units or interpreting data. Having confidence in your maths skills will get you a lot of 'easy wins' in your physics paper, and it's maths revision for free!