1) Find your motivation!
Whether it be video games, a reward, money--- find something that will drive you to achieve your goals (in this case, school work)
2) Understand the why behind school work.
Often school work can be a bore or a pain to do. Yet it is something given in order to help YOU the student! Whether it be class work or homework, it will benefit you in the most ways possible (EVEN if it only helps you for as much as a day to several years).
3) Don't get distracted!
Usually, most of us would like to take a break and watch a movie, play games, sleep, or read a book. Stay away from these 'obstacles', tell yourself that once you are done with all your work, you can proceed to do these things.
4) Study, study, study!
Now that you have your school work done and out of the way, you can review it over or learn relating topics to it. Write down any questions you may have and ask the teacher about them during their free time. If you really want to be on top, then study ahead! It won't hurt you to know things a little head of time before your classmates do.
5) Stick to your plan.
This is the most vital step. If you don't follow it, you'll be behind in your school work again! Make sure you find that motivation or something that you strive for :)