As your gcses are in two years, don’t stress yourself out too much because then you risk burn out which nobody wants. Do little and often by making flashcards/mindmaps on topics, completing every piece of homework and asking your teacher to explain things you don’t understand (especially in maths)!! Make sure to revise for any topic tests/mocks. I improved my maths grade by asking for help and doing exam questions (but you might be too early into the course to do this) so maybe ask your teacher for some extra resources?