I think one of the things that helped me throughout high school was starting to keep a calendar. Have a monthly calendar in your room or in your phone that highlights your day to day tasks (Sports, Birthday Parties, Doctors Appointments, etc). in one color, maybe school assignments (Tests, Quizzes, Meetings) in another so that you have a general lay of the land at least a month at a time.
Then, It would be helpful to have consistent and specific times each day that you do repetitive tasks. For instance everyday after school in highschool from 4-7:00 I sat down and did homework, college research, SAT prep. I had that time blocked off everyday for myself to get that work done. If you finish before? Great. If you have to go later? That's fine too. It's jsut nice to know that you have that time every single day to work an get things done.
Try keeping a planner or a to do list. In my experience, the most satisfying feeling in the world is checking off a task on your to do list want watching it get smaller and smaller! :)