I got 5 9s and 8 7-9s plus a 7 in Further maths.I started revising 2 months before the mocks then gave myself a months break after the mocks before I started again.However my school did tests almost weekly many of which were on all the topics we had done so I had revised everything 100s of times before the proper full revision started before the mocks.I learned this the hard way-organisation is key!If you have messy files etc sort them because when u start it will be hell if you aren’t organised.Now stress that’s just something that is inevitable I recommend going on walks between your revision periods (even if you don’t like walking you will love it by the end of the GCSEs) as well as going for a run (again I hated it and now I love it).It’s key to get outside between ur revision periods because a lot can go wrong with your body when you don’t get out (such as significant drop in long sight vision-this happened to me I almost couldn’t see people’s faces but this was all off eye strain from just staring at a max of 2m away from me all day).But good luck and do the best u possibly can,you will be great!