My biggest tip for studying would be to follow up with things that you don’t understand as you’re learning them. For example: if a teacher explains something in class that doesn’t quite make sense to you, don’t wait to “figure it out” before the test.. Instead, go back and read your textbook and ask your teacher while you are in that particular chapter/lesson. That approach will help you so that you are building your knowledge as you go and not panicking at the last minute (I can testify this from personal experience).
It is normal not to understand many of the concepts, especially in science classes the first time. Many of the concepts are complex and require thinking about them and processing them quite a bit. There is no shame in spending extra time to truly understand a concept. Thinking about these topics and truly understanding them will help you to apply them to real questions especially if you want to stay in the sciences in the future 🙂
My take would have a discussion group with friends, ask questions in areas you are not sure of, you can have different books as opposed to those given at schools for additional reading and also check past question papers regularly