Using your existing GCSE physics textbooks will show you all of the information that you have learnt over the past two years of study. Have a look at the contents page to see all of the material you will need to revise. For example, first chapters in GCSE physics textbooks will usually be about the structure of the atom, so make a plan of the timetable your revision is going to take, starting with this. Keep this bit simple as there will be a lot of material branching off from this one subject.
Making notes is very important, perhaps you will never look at them again or you may use them as your primary source of revising. Either way the very act of writing something down helps you to remember the piece of information more clearly. You do not need to write absolutely everything down, it should be a summary and as long as it is going to prompt you to remember the main points that should be sufficient.
Learning from your GCSE physics textbooks can be too linear and quickly become tiresome. It can seem as if you are having to learn everything all over again. A better way, depending on your preferred style of learning, is to use mind maps. These allow you to write the main subject in the middle of the page and branch off with information and additional notes. Even better, get yourself some mind mapping software. Free to download from the internet, although purchasing some software will get you additional, useful features. Software such as this can be helpful to your revision as you can look at the subject and follow a better structure of learning as all of the relevant information will be grouped together. Many software companies will also provide the software for your mobile phone or other portable device, enabling you to revise wherever you are without carrying all of your heavy books around with you.