For English it pays to read at least some of you prescribed texts in the summer holidays. For most other essay subjects (eco, legal etc) the content is reasonably straightforward and you should be able to learn the prelim content fine at school. The differentiator for these subjects is memorising stats/doing revision come exam time.
Exactly this for Economics and Modern History (from my experience). The early content for Economics is quite easy (comparatively) but you'll find that most people will not be able to express their ideas quickly or concisely enough in the allocated time. English Advanced can honestly get shafted, I'd place it up there as one of the most consuming subjects in terms of time and effort. Don't crap yourselves for the initial year 11 mathematics, both Advanced and Extension 1, there isn't really any need to look far ahead. However, make sure you get perms and combs, and if this year's Ext. 1 is anything to go by, learn Binomial Expansion Proofs and those aforementioned topics well!!
Overall, don't stress too much about prepping. The courses are designed with your anxiety in mind and start off easier, as you'd expect. Make sure you can find a balance between your cocirrcular and academic commitments, the preliminary year is a good time to work this out if you make the effort to properly apply yourself. This will help you once the pressure builds with multiple assessments, however, this year you can afford to make mistakes and experiment with preparation with relatively few consequences.