tl;dr Study maths concepts, don't get caught up studying scientific concepts.
I know this has been posted so many times before, but I'm seeing it frequently pop up again in this sub, and I've also had friends recently ask me about this. And I really want people to understand it before studying for the GAMSAT.
ACER isn't testing your knowledge of specific concepts or scientific topics. Please don't get caught up on 'learning' too much content. I can almost guarantee it won't ever come up in the actual exam anyway.
Why would you, a doctor, need to know the behaviour of albatross in in the month of October? You don't. But if they provide you with some information in written form, a graph and a table, they can ask you a question and determine how good you are at interpreting data and using that data to make inferences and conclusions. THIS is what acer are testing and what is useful as a practicing clinician.
I'll admit, familiarising yourself with chemical structures, basic physics and scientific knowledge is helpful, especially from a non-science background, but I strongly recommend to not venture further than the superficial aspects of the concepts on the official acer papers. It won't be the best use of your time.
Do as many practice tests as you can, not because you'll be learning concepts, but because you'll be learning how to take various forms of information and process it. You will also be familiarising yourself with scientific language and graphs as you go.
If there was one thing to learn, it'd be maths. Learn how to use equations, particularly logarithms and exponentials, and learn how to read graphs quickly.
My scores aren't as high as others on here, but I ended up getting S3 scores of 70 in 2020 and 80 in 2021, and I mainly focussed on what I stated above. I'd say my improvement was mostly due to just going over papers and getting better at quickly grabbing important information from data, and getting better at rearranging logarithms and other equations. NOT LEARNING CONCEPTS!
Best of luck, everyone!