1. reading/exploring widely
this is, in my opinion, probably the most underrated technique. the hsc syllabus often seems quite limiting in its scope, and to be honest it is, but looking at other sources can be super helpful. even just watching videos on other countries' high school syllabus can help a lot, as they often provide alternative perspectives that allow you to approach questions in many different ways. for example in physics, hsc teaches all of the concepts without calculus, but understanding how many formulas came to be by using calculus definetly helped me to understand what they actually meant. first year university content can also be quite useful too, such as for combinatorics in extension 1, since these ideas are universal and its not like the hsc is the only one to be teaching these topics (would recommend this video if you're struggling with combinatorics:
). having an additional layer of understanding is also great to provide some higher level information, just make sure its not too overkill, but again first year uni content is typically quite safe.
2. fundamentals first, then all else and always link back
unfortunately in year 11 i decided to pick 3 sciences, though i eventually decided to drop to only take physics. chem was literally the worst class ever for me, and in hindsight its because i really neglected to fully absorb the fundamentals, not only in year 11 content but also year 10. the fundamentals are super important, such as for chemistry: what is an atom, molecule, chemical, isotope, etc. its really easy to just gloss over these simple defintions and terms but they will ultimately screw you over later, as everything else naturally builds on top of this. for example my first chem test was on all the decays of nuclei. i recall there was one question asking for one isotope that was used in medical industries, and in my response i referred to the isotope as an atom or element or something, causing me to lose a lot of marks on a 7 marker. these terminologies are super important not only for your responses, but also your understanding, because they are so fundamental to the subject.
now i am not an expert at chemistry at all but id say that there is probably some basic notion of reactivity that was taught very early on in the syllabus. it is quite easy to be ignorant of these small details, but definetly make sure you understand why reactivity differs, what factors are at play, etc and make sure to connect everything back to the fundamentals of chemistry, such as electrons in valence shell blah blah blah. if you understand how everything connects back to the basic "axioms" of the subject, then the content will much more naturally make sense and you can better answer any question they give you. eg in physics, always keeping the super fundamental ideas of newtons laws of motion, conservation of energy and momentum, vector and scalar quantity in the back of your mind effectively answers 90% of mod 5 questions, and reduces the amount of mistakes you will make.
3. get out of your comfort zone
a common mistake i always made in year 11 is that i would be quite demotivated to spend time on the questions that i was not entirely comfortable with answering. however, this is probably the most important thing that many people neglect. while yes, it is a good idea to keep spamming out questions in the topics you're comfortable with, definetly spend a lot of time on fixing up the patches in your knowledge, even if its frustrating. for example in ext 1 i would always neglect combinatorics as i would always think that there was a new method to solve every question lol, super annoying. but then approaching the trials i spent all of the class time we had given for revision on combinatorics, just going through the textbook derivations of everything, all of the questions i could find etc and ultimately forcing myself to not just do integration questions or whatever actually made me a lot more confident in the topic, and then in the trials i didnt get any combinatorics questions wrong at all (damn q10 in hsc though).
overall id say that i was also quite similar to you in year 11, especially in the sciences i found it so frustrating that every question seemed to require a completly different approach that seems to appear out of nowhere, as if they are just wanting to you to "use a trick" that doesn't properly test your knowledge. i would say the best thing to do is just to practice as much as you can, expose yourself to as many questions as possible, but before you do that really make sure all of your baseline knowledge is there first, draw mind maps, flowcharts, whatever lets you connect up all of the information in the subject in an intuitive manner and lets you understand how different concepts intertwine and come to be. do not just ignorantly spam out questions, at least in the beginning write down everything you think that could be relevant to a question, what techniques do you think that you could use, also possibly if theres two different methods to answer the question to double check the answer, take your time and make sure you can analyse the question as deeply as possible. also know that memorisation of some things is important, especially in chem, but never ever EVER make the mistake of just looking at a question and going "oh, that looks like a question ive seen before" because that is a big trap that you think will save you time but might end up with you losing all your marks. so always try to look at every question as if you've never seen it before, consider everything before jumping in and answering the question, this way your response will be more calculated.
uhh sorry for the end bit its a bit unclear but hopefully the numbered parts are clear : ) good luck