The generic teacher advice for creative writing to to focus your piece over a short amount of time, and include details (personally, I was like, "nah, I'm going to challenge the system" and made years go by in my story. Still got high marks). The stories that are written over a short amount of time can't possibly have too much plot going on - and if that's the recommended style to write, then you should be fine!
The thing for ext 1, check the past HSC questions. I'm doing Romanticism, and the past questions sometimes tell us to write in letter form (aka DEAR SIR/MA'AM I FEEL LIKE STARING AT CLOUDS TODAY AND BEING MESMERISED BY NATURE.... AND YOUR EYES, BECAUSE I'M A ROMANTIC AND NOBODY UNDERSTANDS ME). I just read that with a Southern accent and omg-. Most of my class included letters in their story just to cover that aspect. Maybe there might be a little trick in whatever module you're doing, too.
The biggest things for creatives is that it needs to be easy to read (read: doesn't leave the marker wondering what you meant) and use big words (legit). It would be a pretty cool challenge, actually, for the discovery story if the letter count for each word didn't go over 5 letters. Wouldn't dare do that in ext 1. But seriously, we could look at Scrabble sites for the most unheard of 5 letter words, and just make the writing sophisticated by using those. I might do that now, just to play with my teacher....