I agree with most of what
@EdgeHillStudents said, but I have a few things to add.
But first, just to restate what they said, past papers are probably the best thing you can do to improve. They should compose a major part of your revision scheme.
Further maths:Past papers as before, but my personal favourite for this subject was 'first class maths' on YouTube. They teach you precisely what you need to know for the specification, and in the depth that you need to know it, in a very easy to understand way. I basically just binged their entire Further Maths series a few times and once before the actual exam, then walked out with 93%. Imo easier to revise for than normal Maths. The link to their full playlist on Further Maths is
https://youtube.com/playlist?list=PLJ6MxZJs9Ht9B4ZOxMQA8Qw4XQKOwae2q&feature=sharedEnglish:Just do loads of past paper questions and get your teacher to mark them and give feedback. Also-off heart as many quotes as possible. Don't get caught in the trap of "its not possible to revise for English". Yes, it is. And you won't get a 9 unless you do. As
@EdgeHillStudents said, Mr Bruff is great (I for one did get the chance to look at his content before the exams and it was very useful).
Computing:I understand people's revision styles are different so this varies, but in my experience Seneca is not as good as some of the resources I've seen and used. My main issue is that is basically just tells you the answer before it asks you to answer a question, which I don't think is a very good way of learning information. Maybe its just me though. In my experience, Isaac CompSci is pretty good, but I'd generally stick to past papers on this one.
Also, I don't know what your exam board is, but if you have AQA consider yourself lucky. The specification is basically just a checklist which is perfect for preparation. If you have OCR you can cry yourself to sleep before the exam.
French:Duolingo is king. Cultivate a streak - It will do wonders for your writing and reading papers. Listening and speaking may require extra work though.
Generally:Your teachers are the (second) best resource you have. Use them to mark papers, or check you have self-marked correctly, or to go over certain concepts again.
Good luck!