I'll start with Physics because this is one of the 'weird' subjects. The best piece of advice I can give you is
understand. I don't think I can stress this enough, but learn to understand. It sounds pretty simple at first (and took my whole VCE journey to finally realise) that the key to doing well in Physics is to understand where things come from, how it happens and why it happens. In conjunction with this, what I'm about to say is quite childish in a way, but just play, question everything and enjoy learning. (Every morning before school, I just go to the Physics room and play with anything I can get my hands on).
The one good thing about this subject is that nearly everything you learn can easily be demonstrated in real life and I highly recommend that you try doing everything you learn and applying it to real life. In terms of preparing yourself for VCE Physics, it's probably just getting your basic maths up to scratch (you really only need Year 9/10 maths) and if you want maybe a little headstart, understanding words like position, velocity, acceleration, speed, displacement etc. I went into VCE Physics with 0 Physics knowledge (I still have no clue what made me pick it) but I can 100% guarantee that you will be fine!
An example of what I mean
Pretend you throw a pencil up in the air; is the pencil experiencing a force? what is the acceleration the pencil is experiencing? What is the velocity at the top? Are they the same? Why/why not? Can you tell me why the pencil comes back down and doesn't continue to keep going straight up?
Questioning everything and trying things out for yourself rather than listening to someone/looking at a textbook gets you very far in this subject.