Hi Mina,
My first english SAC was the creative, now I am no exceptional student but I did get an A.
So take this advice as a grain of salt.
Firstly the most important thing is to have a very strong knowledge of the text, I suggest reading it (at the minimum) twice.
The next best thing you can do is recognising the writers style, you will need to replicate that when writing a creative piece, do they often use metaphors?, do they have particular ways of describing things ( for example, my text was Flames by Robbie Arnott, he would describe humans as "apes" and there were many "Gods" that were various animals/seasons/environments)
So when you go to write this creative you want to do it in the style of the author, meaning their use of language.
Now, the prompt. I chose a prompt where I wrote creatively from third person of a character that was mentioned but not really explored in the orginal text. I think the best way to go about prompts is pick the one where you feel you can write the most about, that way you won't feel as if you are struggling to find things to write about.
Obviously I do not know the conditions your school has set for this sac, but if you do get the prompt early I would suggest to write out a whole essay if you can and edit it until you are happy, and try to plan out each paragraph and memorise the key points you want to make. Some people may prefer just to plan the essay if they get the prompt early instead of writing it out, its really up to you and the time you have available.
Good Luck!,
Hope this helped a little 🙂