Any advice for good creative writing? I have my English language GCSE tomorrow

Exam writing and fiction writing are different. Exams are for you to show off with. Fiction is about affecting the audience.

I would say for your exams focus on demonstrating what they want you to rather than trying to be “good”.

Same for any education really. I have thoughts on exams in general. (though to be clear am massively in favour of teachers and education in general)