It's not just assignments too, sustained effort in terms of understanding and applying content, completing all classwork to a high standard and taking notes throughout the term is gonna help you out big time. It frees up time for you to study for your exams when they come up, and by then all you need to do is revise (unless it's an assignment). It also puts you in the right mindset before an exam, minimising stress because you KNOW you can do it. If your assignments come up before your exams, getting them out of the way ASAP will be key.