Exercise regularly. You'll feel better and be more prepared to handle problems.
Eat healthy. Avoid too much sugar. Focus on fruits, vegetables, whole grains, and lean protein. When you're stressed, you'll probably want less-nutritious comfort foods, but if you overdo them, they'll add to your problems.
Try to manage your time wisely.
Say no, where you can, to things that would add more stress to your life.
Make time for hobbies and interests.
Get enough rest and sleep. Your body needs time to recover from stressful events.
Don't rely on alcohol, drugs, or food to help against stress. Ease up on caffeine, too.