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Although Prelim results are not counted towards the final HSC mark, Year 11 is actually a very important year for you to experiment with different study habits and find the right one that suits you the best. Besides learning to work most efficiently, a lot of what you learn in Prelim becomes the essential foundation work for HSC, I don't know about Business Studies or Music, but it certainly is the case with Maths and Chemistry.
For Maths, do the homework your teacher sets you, if there's a problem, never be afraid to ask, who knows, it could well turn up in your next exam!! Make sure you get as much practice as you can, because knowing how to do the questions isn't sufficient, you've got to work very fast AND accurately as well.
For Chemistry, write dot points. start with one textbook and then move on to get a more comprehensive understanding by looking into other textbooks. The easiest marks in Chem are the calculation ones, eg moles, heat of combustion.
For English, read widely to improve expressions. I don't think you need to write an essay/week for Prelim yet, but it definitely is advised for HSC.
I'd say you need to spend about an hour for each subject, but be flexible. Devote more time when assessments are coming up. Good luck!