Draft essay, rewrite, draft essay.. rewrite! There is no shortcut to English just like most other subjects in the HSC, it takes diligence and patience to become better. If you are struggling with English I highly suggest getting a private tutor to help you guide your way through the course as this subject may iffy sometimes.
To create an essay I suggest reading the book first as this would be the most obvious thing to do. Then construct a TEE Table (Technique, Example and Effect) and finally practice crafting your essay, if you have a tutor it will be a lot easier to piece together! Make sure to memorize your techniques for the HSC exams, know your themes inside out and know how to answer short answers as this will be the first thing you come across in the HSC Paper.