I wish I was told that English was compulsory lol. JK I already knew but it's seriously a pain in the ass. English took up the bulk of my studying, easily 40% of it, and it paid off, I ranked 9th in the grade. Everything else had the other 60% to contend for my attention. So I guess time management was a minor issue, but it's more to do with how productive the time spent was- I probably do fewer hours of homework than others, but I tend to stay on task.
Ext. Maths isn't that bad, though it requires the attention of a 2 unit course even though its only worth 1 unit. It's actually quite interesting, once you get the harder concepts though! 2U Maths will feel like a walk in the park afterwards.
Biology was the subject that I spent the least time on, and I warn you now that the Year 11 course is half interesting (Patterns in Nature and A Local Ecosystem), and the other half focuses on evolution and australian plants. That was boring as bat shit but I'm told the Year 12 course gets better but it was my lowest ranking subject so I dropped it. Whenever you study for Biology, make sure to remember examples and specific details about them- there's always at least one question.
Chemistry was fun- and tbh I liked the calculations involved once you got what you had to do. It's hard I guess, but not really at the same time. If the concepts click with you immediately, then it's not that hard. The one thing I remember from last year was my first chemistry lesson where our teacher greeted us with: "Chemistry is a hard course. Half of you will FAIL!"
Practice questions are the best- honestly don't start doing them a day before (like me) because they really do force you to retrieve archived or forgotten knowledge.
Good luck in your Prelim year, take it as a test run but don't stay at home and study your ass off. It's more about the work ethic, time management and skills that you develop now that will carry over into the HSC year.