Keeping your motivation up is the most important thing if you want good grades! Here's a few ways to do so:
Reward yourself (food, new book, an episode on Netflix...)
To-do lists: achieving smaller goals will keep you motivated
Think of what you want to achieve and how to get there
Remember to relax and forget about school once in a while
Start the work immediately
Stop making the mistake of leaving something for the night before. It's going to be so much easier if you start working on an essay or a project right away and do a little bit every day.
Get a planner / bullet journal
This is a part of staying organised. It's good to have every event and due date written down even if you use the calendar on your phone. Furthermore, bullet journaling is an extremely fun and relaxing hobby!
Listen to instrumental music while you study
Music can help you zone out other distractions and focus on your reading/work, but make sure it doesn't have lyrics, because then it might have the opposite effect. Spotify has a lot of food playlists dedicated to studying and staying focused.