Work hard and play hard. Many students I know were doing well with 2-3 hours of study per day and managed to keep a balance with co-curricular activities. Crank it up when exams are approaching - especially before Trials and the Final Frontier. Some subjects (e.g. maths, sciences) need a consistent baseline of study throughout the year, whereas others (English, humanities) will need you to keep refining drafts of essays and creative works. Where relevant, keep a folder of notes where each syllabus dot point receives about as much attention as you'd expect in the HSC exams. Don't waste time with anything that's outside the syllabus. And do lots of past papers.