English and ext. 1 were my best subjects but I have to admit that compared to other subjects, I really didn't do much for them. Year 11 was a blur but I guess you might want to focus on essays and narratives. Essays were only lukewarm to me in year 11 and it took some experimenting before I wrapped my head around them. Narratives are a bit more of an acquired taste. Make use of your year 11 assessments to gauge how well you do in both, if you're in need of massive improvement or just some tweaking. That should give you a measure of how to approach year 12. Listening in class is important. I would say write notes on your texts. If it's a book, mark out useful quotes. If it's a film, rewatch it and comb through for quotes and techniques like music, camera angles, etc. Usually, HSC English is about themes, so keep particular themes in mind when making notes.
I found it helpful to write a practice essay before in-class assessments. I don't know how I did it, but I wrote 'general essays' that I could memorise and tweak for the essay question. Worked for me but not recommended right off the bat. Everyone studies differently. But the most important thing is to know your quotes and techniques. They make up the bulk of your essays. You might like to approach narratives with characters and plot already in mind so you're not grappling for straws during reading time.
Preferably make notes on your own. Then look through study guides and notes on this forum and add anything useful to yours. Be confident in what you've written, because in English, you'll need to make yourself stand out from other people who are doing the same text as you, and may have also consulted the same guides and notes as you.
Extension 1 was quite alright for me. It's easier in a way because in year 12 you spend the entire year on one topic. What catches people out is that the topic your school chooses may not gel with you (e.g. there's stuff like romanticism, navigating the global, crime fiction). Do not expect that it will be easy but do not fret about it. You will find out if the course is for you soon enough. Some people drop out because they weren't prepared for ext 1 and made the wrong subject choice. If you find ext. 1 okay, then I recommend that you study the way you do for advanced. Develop your own studying habits (admittedly, mine was last minute study - regularly revising was useless to me), know your texts, learn from your mistakes (do not be disheartened by one bad mark in English) and just be confident even if you're not. At the end of the day, you're trying to convince markers that you know your stuff.
Good luck!