Exercise regularly, everyday if possible for a minimum of 20 minutes is ideal.
Get sufficient sleep.
Create a daily routine for sleep, meal times, exercise & completing school work. This will assist your ability to stay calm and give you a feeling of being in control.
Make time for yourself each day by doing something you enjoy and that encourages relaxation and or fun.
Be proactive. Anything you can do ahead of time as tests, assignments or exams are approaching is very helpful. This can be having bills paid, booking time off from your job, preparing meals ahead and letting people know your availability during these times.
Learn mindfulness exercises. (breathing, visualization and muscle relaxation techniques)