Hi!
I'm currently enrolled in 3-4 methods, but I can tell you I struggled in 1-2 as well, and am glad to say that after fixing my study habits and the way I approach methods, I've improved by heaps.
The first thing I can say is practice practice practice!! Methods, I've found, is less about knowing what a formula is (after all, you get a formula sheet on the exam!), but more about knowing how to apply formulas. In unit 3, the SAC is an application task, and unit 4 from what I've read and been told is a problem solving task and a modellin task. All of these, require you to use mathematical skills in a different context. Find any and all practice tests or exams for your SACs, or even ask your teacher! If you use edrolo at your school, do all the practice tests and questions on the lessons! They help a lot, and be sure to go through the solutions.
One other thing that I did was finding as many different resources as possible. My school uses the Jacaranda Maths Quest, which I find personally to be hard to understand, and typically assume that you know all of the pre knowledge to learning a new topic. I bought the Cambridge textbook for myself as I had heard from many that it was a far better resource, and in my opinion, they were right! Like I mentioned before, edrolo is really good as well, but if your school doesn't have edrolo, try mathsmethods.com, khan academy, or even just attending methods lectures. Understanding a topic properly will really help you do well in methods, especially as you come up to some more challenging topics in unit 2, or build upon skills in these topics in 3-4.
One more thing, not necessarily for your SACs, but MAKE YOUR BOUND REFERENCE EARLY!! There is nothing worse than rushing to make a boudn reference in the week before the exams (if your school does unit 1-2 exams)
I hope this helps!