I did both English and Lit 3/4 this year and I think its great that you are asking this because a refined vocabulary will set you apart from the rest of your cohort.
The best thing you can do is READ. I know everyone's already said it, but I'm going to say it anyway

My lit teacher said this to me at the beginning of Year 11: "The mind is like a sponge. Exposing yourself and immersing yourself in the works of more superior writers will, by default, challenge you and force your own writing to improve". I found this the best piece of advice I received from my teachers. Reading, avidly reading, other author's works will result in you absorbing parts of their own style and vocabulary.
So READING is essential. However, personally I think its a bit late in the process to spend your time reading through greats like Tolstoy - instead of reading unrelated (yet brilliant!) novels by such authors, I'd recommend getting onto the internet and reading
relevant analytical essays written on your school's set texts. This will expand both your knowledge of
your texts and the complexity of the ways in which you approach writing on them.
Then there's the writing component. Pretty much self-expanatory. Write as many essays as you can, trying to avoid the easy topics after the first few weeks of school. If you train yourself to write on difficult concepts that force you to really think, you will find that your SAC topics will seem comparatively easier to tackle.
So my main piece of advice would be to read critical essays written by scholars on the internet. Google Books is a good resource that I found helpful in Year 12.
Best of luck!