to get into B Psychology you need a fairly high ATAR, 90+
to get into a B Science majoring in Psychology you dont need such a high ATAR (70-80ish depending on the university) but you will need to get a credit average to do honours at the end.
you will be doing a lot of writing in psychology, so english is the main subject you want to have on your side going into uni. they will cover the science stuff that is relevant to psychology in 1st year. having some maths skills would also help with the statistics courses
As said, you will be doing a statistics course at least once every year, thus maths is useful at least a 2 unit level.
Depending on what area you plan on going into, biology and to a lesser extent chemistry can be useful. There's a lot more to psychology than just the clinical/therapy side (from what I remember, about 52% of graduates with a degree in psychology don't actually become psychologists).
English is obviously useful in every university course, and since psychology is partially a social science, essay writing skills are a must.
