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. :)