The best thing you can do is consume content to do with the revolutions you will study.
If you are studying the French Revolution, I would recommend Christopher Hibbert's or Eric Hazan's 'The French Revolution'. Both books aren't too dense and will give you a good overview. I would also recommend my own podcast titled 'Grey History: The French Revolution'. Written by a former VCE student, its deigned for people coming in with no background and full of primary source quotes and historiography which can use for your essays.
For the Russian Revolution, Sheila Fitzpatrick's book 'The Russian Revolution' is also a good summary book. If you're happy with something more dense, 'A People's Tragedy' by Orlando Figes is amazing.
Cannot help with the other revs sorry, however, reading a good book or two will do you an immense amount of good.
Highlight short, sharp observations surrounding key events as you go through. These can be used in your future essays. Unique quotes (either primary sources or historian opinions) will help you stand out amongst your peers.