I usually got pretty good marks for my creatives during the HSC so here are some of my tips:
1.Steer clear of the cliches, especially stories about teenage angst. Issues such bullying and body image are very common to teenage life, but it is because they are so ubiquitous that they have become cliches. Unless you think you've got a really unique take on it, it's better to avoid.
2.In the same vein do not utilize excessive drama. Markers like when you communicate complex ideas in a nuanced and sophisticated way and things like car accidents, terminal illness, gun fights, government conspiracies etc may hamper your ability to do that. Not to say you can't have elements of these things, but make sure you use them sparingly and think of the meaning you wish to convey underneath your plot.
3.Focus on a moment in time. Being a short story, you do not have the time to weave together a grand narrative about a person's life. Instead, pick a moment and exploit the emotions, actions and reactions associated with it. It can be anything from a conversation to a character writing a letter. Either way, it will drive you away from the 'plot' aspect and allow you to communicate more multifarious ideas.
4.Choose a different context. That has been my golden rule. Choosing a unique setting, whether it be a different culture or different time, is the easiest way to set your story apart. However, make sure you are knowledgeable about your setting so you can set it up authentically.
5. Begin by briefly setting up the scene, these do not always have to be descriptions, you could give subtle indicators as to the location.
Hope that helps and best of luck
