When students ask me what's the first thing they can do to succeed in school, I reply: Get organized. When most people consider the concept of getting organized they think of clearing out physical clutter. Cleaning under beds, organizing drawers, creating files to sort papers are all the sorts of things that come to mind. Certainly that's a critical part of getting organized, but we also must organize our tasks, priorities, and use of time.
Knowing what you need to do is the first step in getting organized. Make lists for personal tasks, class-related tasks, course assignment tasks, and so on. Then allocate time to each task. Create daily and weekly (and perhaps monthly) to-do lists. Create and maintain an academic calendar. List exam dates, assignment dates, holidays, and your own personal deadlines. Keep your calendar updated and revise it as needed. If you prefer, you can organize your semester by week using a 1 page-per-week planner.