trying4JMSS If you have any good (and hopefully willing) english tutors/teachers, try writing some pieces in a timed environment and sending them over for advice/tips!
As for things you can do by yourself, try work on idea generation by taking inspiration off other sources of like content/media (movies, tv shows, books, etc) but not too heavily
Make sure you have a good structure/plan, like how you'll sort the story out. Flow/timing is very important and it's ideal to go into the right amount of depth while not making it extremely complicated
I've been told it's good to include a moral/message/connection to a real world problem or something similar, just to make your story more advanced and therefore grant you higher marks
Wishing you the best of luck!!