I would suggest that you become familiar with future topics. Dont study topics you have already done in class, because trust me; you will know them back to front by the end of the year, and you will waste your time studying them in more detail now.
Look at the syllabus; dont worry about the textbook as they often put other stuff in, and this can be peripheral to the main point of this exercise. The point is to become familiar with the content so that when you study the course in class, you feel comfortable with it before you even begin.
I know that many students would still be finishing off the BOP work. The BOP is probably the most challenging concept in the HSC course, purely because it is technical, quite abstract, and you have never seen in before. So perhaps in breaking my first suggestion; you could study that if you are not on top of it.
The rest of the course is mainly issues and economic policies. Essentially the two topics are interlinked. Economic issues presents a common range of problems facing an economy, and the last topic is essentially a synthesis of the policy tools available to overcome these challenges.
Dont worry about learning historical facts, or a history of Australian policy, because that will come later. Just sift through the syllabus, look at each dot point, and try and find out what it means (you might use a textbook here). But yes, once again, dont use the textbook as a guide of WHAT to study, just use it as a reference as you will waste your time.
Shuning is also right about practice extended response questions. See if you can get access to the standards package (your school should have it). Take a look at some band 6 responses to past HSC questions from topics one and two. This way you will start to see what makes a good HSC response. There is a very specific style that markers like to see; so it is worth checking out. You dont necessarily need to go and write heaps of responses, but try to practice writing responses with the stylistic attributes in mind.