Two things I'd suggest. First, take a look at your goals. If you don't need that high of an ATAR, then there's not much that will convince you to study. If you have an ATAR in mind that is pretty high, then you have no choice but to study. Try to talk to yourself as if there is no way to achieve the goals you have without putting in the work.
Second, try to do things you like and then study. For me, I always enjoyed going for a run before studying. It helped to relax me and convinced me to study more. Even if you can only do 30 minutes at a time, it's better than nothing.
Maybe try a plan like this after school:
Eat (30 min)
Activity you like (30 min)
Study (30 min)
Break (15 min)
Study (30 min)
Activity you like (30 min)
Study (30 min)
Break (15 min)
Dinner and chill (1hr)
Study (30 min)
Following this, you'll get 2hrs of study done each day, which is pretty good as well as 2.5 hrs of relaxing.
This being said, though, at the end of the day, the only thing that will keep you working is discipline. At some point in yr 12 you'll experience a feeling of not being bothered to study, especially when you feel the study isn't getting you the results you want. It's at this point where you either make the breakthrough or you become like everyone else.