Hey Karen!
This is a really good question and I've been asked it before, so I'm really glad you've posted it here so that I can respond in a way that lots of people can see.
Basically, the preliminary course is built to give you the foundations of the legal system. Some parts of the syllabus for preliminary exist because without studying it, you would have a gap of knowledge, even if it isn't something you will be tested on in the HSC. Other parts of the syllabus are there because you absolutely need to know certain things for the HSC course.
I've got the syllabus in front of me so I'm going to kind of scroll through and point out parts to you that I would make special note of - perhaps putting your study notes for this in a separate folder, or putting a star at the top of the page, or something to signify that these notes are likely to be used in the HSC.
Basic Legal Concepts: You need to know this all pretty well back to front. The reason being, you need to UNDERSTAND this more than you need to memorise this. Ideas about values, ethics, fairness, equality, rule of law, etc, will be the basis of many of your legal arguments in HSC essays.
Sources of Contemporary Law: I would definitely take serious note of this part. PARTICULARLY the division of powers and the separation of powers. You will be doing yourself an enormous favour by getting your head around it in year 11, because it comes back up in HSC and people are still confused by this concept.
Classification on Law: This part of the syllabus is kind of existing as a "filling the gap in your knowledge" kind of thing, and probably won't be deeply relevant to the HSC course. In saying that, I don't recommend skimming over anything, because legal studies has merit beyond the HSC, and this part of the syllabus is relevant for life.
Law Reform: Definitely pay really good attention to this part. In your notes, build up this section as much as possible. Include as much law reform as you can - and find law reform that really interests you! Law Reform is a key theme/challenge in the HSC syllabus, so give yourself a head start here!
The Individual and the Law Topic: This is a great topic because it brings you into the system, and it is no longer just words on a page. Enjoy this topic.
Law in Practice: I hope you find the topic that you choose to study to be really interesting. Personally, I studied Women and loved it. This is an important part of the syllabus because it gives you the opportunity to step up and say "hey, this is really interesting, legal studies is actually super duper relevant."
Enough syllabus waffle now! About study notes: Give it a good go! Preliminary is here so that you can play around with how you like to study. Find out if making study notes on palm cards works, or if you need to make timelines, or graphic organisers, or simply a word document! Make the notes as detailed as you can with contemporary cases. If you need to cut back on content, but it is committed to your understanding rather than memory, that's cool. Reciting words won't help you in legal, when your competitors are showing a thorough understanding of notions. The best part of the syllabus for doing your own exciting research is in the Law Reform topic.
Basically, Preliminary is a time for you to give it your best shot and find out what works for you. The fact that you are on this website asking questions says to me that you are super keen, and that is the key to succeeding in year 11. You need to go into the course like a sponge and be ready to take in as much as you can.
Deep down, I feel like you could do the legal studies HSC course without having done preliminary. But it would be, really, really, really, really hard. You build so many great legal skills in preliminary that you just wouldn't have the time to develop if you only did the HSC course. Preliminary is a time of trial and error. You'll do great! Let me know if you have any more questions