1. Stress ~ Stress, you can try getting some space, walking in the fresh air, and just relaxing.
2. Eating Habits ~ Eating habits, you can try a new diet, substitute healthy foods you like.
3. Physical Activity ~ Physical activity, buy a gym membership, join a club at school or jog.
4. Sleep ~ Sleep, learn time management; get to bed on time and wake up early.
Hope I helped. :)