Hi!
There is no one 'secret' but I can certainly give you some tips. These tips are often heard, but of course being conjuring up some motivation to follow through with them is the major obstacle. Start studying early. Accelerate yourself at home by reading the textbook and keep yourself 2-3 weeks ahead of your school's pace. Psychological research has demonstrated that when you learn the same thing twice in different settings (separated by a time gap), memory retention is improved by a huge amount.
Many people love one subject and focus all their attention on that one, as if to ensure they come 1st in that subject in their class, at the cost of the other subjects which they less care about. This is a poor strategy as your worst subject determines your ATAR more than your best one. I would have been more satisfied coming 2nd in everything than 1st in a few and 10th in the rest. In line with this, do more than 10 units so your worst subject is automatically dropped (except English). My policy was to prioritise my worst subject at any time (which is often a slog) until it is no longer my worst subject. This process of self-improvement will gradually improve your expected ATAR.
In terms of home study, motivational management is critical. Begin the day with your least favourite subject. When you get bored of it, don't go and watch TV. Take a break from your least favourite subject (English for me), by starting studying something you prefer (Physics for me), and perhaps conclude with some Maths practice before taking a break.
Overall, in spite of these tips, the main secret is to develop much more motivation than students around you, and study hard with the goal of achieving the best mark that you possibly can.