I got 20s for all my pieces this year except one, and I just memorised quotes for essays and had an idea of some techniques I wanted to use in my creatives so i can be more prepped for the reflection.
It does not matter what percentile you are in order to get 20, it just has to meet the criteria and concisely reflect the question/stimulus. For reference, in my school trial, the modal mark was like 18.5 and around 20 people got 20 for a Module essay... you shouldn't be considering the percentile that is only for ATAR
I also would not recommend memorising for creatives as it will most likely not relate to the question and you will therefore be stuck in the exam and have nothing. So instead of gambling on whether the question will link to your pre-prepared, just practice doing unseen texts to get better.