its really simple. more simple than all of this stuff.
1. You have to listen in class and trust that the teachers know more than you cause they do. If they tell you you should do something then do it, no questions asked.
2. Have consultations with your teachers about exam marks and where you can improve. They know everything there is to know and so they are your best resource.
3. Do the work. I don't know what subjects you are going to do but I'm doing a random selection (eng adv, sor 1, maths ext 1, french cont. and art) so its pretty diverse but all of the study methods are similar, you just have to work, do essays and give them in to your teachers and ask for them to be marked, then you will figure out where your problem areas are and what needs work.
Good luck and most of all enjoy year 12 its the best year of school by a mile so don't just make the year about a number cause its not worth it