This is what I can think of at the moment- I hope it helps!
Make small, regular goals that will keep you focused and motivated on work- be specific so that every week you feel you have accomplished something, and you're that one step closer.
Pace yourself- the first 2 terms are full of assessment tasks. Start early and keep your head up about weeks that will be full of due dates. In the more quiet weeks, use them for study/work etc. because you'll need them!
Have things to look forward to, both in the near and distant future- organise to do things on the weekend, make plans for schoolies and uni etc. so you realise that the HSC isn't the be all, end all, and there's a reason for the work- having more choices for uni etc.
If things start to get tough, SPEAK UP! don't suffer quietly! Talk to your friends, parents, and there are always individuals at your school that will help you- teachers, year coordinators, careers advisors, counsellors. Thie year is about YOU, and you need to do everything you can to help yourself.
Keep healthy- people always say this and often people don't understand why it's included in year 12 tips, other than because it's common sense. It's because the healthier you are, the better you are able to study and balance your life, and the happier you will be. Sleep 7-8 hours a night, get exercise (really helps burn off stress), get out in the sun- seriously, it's great to study but you really need to take breaks so that you don't feel like an anaemic hermit.
Don't compare yourself to other students- it makes people unecessarily competitive, and often makes you just doubt yourself. Everyone works differently, so just make sure you're doing what you have to do to do well.
Communicate with your teachers well and often- check in with your teachers every 2 weeks or so, show them your summaries. If you show them you care about your work, they will be more willing to help you do your best.