Chemistry has been regarded as one of the most difficult subjects in the HSC, due to the amount of content and the nature of the application of its concepts. However, just as with every other subject, the way in which you revise the content and consolidate your understanding of the various topics will help you stand out and maximize your marks. As much as it applies for all HSC subjects, familiarizing and following the syllabus is especially important for Chemistry, as essentially all of the questions in your final exam will be some variation of a syllabus dot point (or occasionally even just the dot point itself!).
Hence, a crucial starting point to maximize your chances of success is to make notes that directly address each and every dot point of the syllabus (note that due to the nature of the content in Chemistry, I.e. writing out chemical equations, drawing diagrams etc., hand-writing your notes may often be a better way to consolidate your understanding). After you have completed your notes, the next step is to apply this knowledge through attempting practice papers. Keep in mind that past papers should be done in exam conditions in order to maximize their effectiveness.
After you have finished a past paper, go back to what you have done and highlight any areas where you have mistakes/are conceptually uncertain, and note which sections of the syllabus these areas correspond to in order to mark future revision. The difference between average and high performing Chemistry students often boils down to the amount of RELEVANT information that is put down in the short answer section. To maximize your marks in this section, make sure to memorise key phrases (such as definitions, chemical processes and other succinct terminologies given to you by various study resources), key chemical equations, and to know how to address questions based on the verb that a short-answer question gives you (I.e. know the difference between assess, describe etc.).