I left high school this year, after doing the following GCSE's:
English Language, English Literature, Maths, Core Science, Additional Science, History, French, Art, Statistics, ICT CiDA, Physical Education and RE.
The main piece of advice I would give is to revise smartly. By this, I mean that you should adapt your revision techniques to the type of learner you are (visual, audio, kinaesthetic). For example, I am a visual learner, so I mostly used flash cards, highlighting key information, mind maps and post-it notes, and also did past papers to identify my weaknesses. It is really important that you revise your weaknesses the most, I know a lot of people who revised the topics they liked and ended up not doing as well as they should have in the exams. And also, do not rely on resits, they may seem like a back up, however it means more exams to sit, so less time to revise other subjects, and no matter what grade you get in resits, you have to keep it, even if it is lower. All the hard work will be worth it in the end, I'm expected to get A*A*AAAAAABBBBB and I and I feel like I revised well. Just keep motivated and you will be fine.