Well, the psych course is changing next year, though I don't think it's gonna be a huge change, so I won't be able to give you a complete AoS to AoS run-down. Also depends if you're in year 11 or 12. I'm year 11 this year, and finished psych 3/4. So this is from my POV.
You should definitely start during the summer break, but you don't have to go all hardcore. Attend some of the summer holiday lectures maybe? I went to tsfx, and they gave a run-down of unit 3 and unit 4, along with 2 thick booklet of notes per unit, so I found that a pretty good introduction. Start with that first, then if you think you don't want a life during the holidays, you could start reading up on next year's textbook, make some notes and maybe even try the learning activities. But hey, I just went to the summer holiday lecture

During the year itself, each AoS requires a different study technique, or in my opinion at least. There are some bits of info. where rote learning just seems to work best, e.g. functions of the different lobes of the brain, advantages and disadvantages of the different scans, etc. Again, I can't comment too much since I'm not exactly sure what's gonna be on next year's study design.
For the SACs, again depending on what kind it is, different study techniques are required. I had to write-up an ERA for visual perception, so what I did was basically write-up a draft, had my teacher look over it, made a few changes, and then I rote memorized the entire thing, either by writing it out over and over again, or just reading it over and over again. If your teacher gives you a criteria sheet beforehand, then you should look over the different criterias and make notes based on it.
To prep for the exams, I would do a TON of trial exams. I'm talking about 20-40 at least, and some people on this board have done way more. But since it's a new study design, you guys would be disadvantaged ALOT. The other thing I did was make my own notes. I'm not talking about brief summaries, I'm talking about COMPREHENSIVE NOTES. I would borrow Psych Notes, notes from my friends, notes I find online, and the textbook, and from that, make my own set of notes. All-in-all, it took me about a month, give or take, per unit. And I would do this just prior to the exam. I really really cannot stress this point enough: Make your own notes. Sure, it's fine to look through the notes of others, but it doesn't help as much. During the process of making your own notes, you're also going through the course another time. You also know how your notes are ordered, what info. you have in your notes, and etc. You'll be looking at it everyday, and eventually you'll know it inside out, and if you're really sad, you'll probably know it better than you do your girlfriend

Last but not least, have an INTEREST in the subject. It's one thing to want to do well, it's another to enjoy it. I absolutely love this subject and found it extremely interesting, so paying attention and doing well wasn't that big a deal for me. If you have the interest in the subject, you'll definitely go the extra mile to get that 50.
Hope that helps!