Dear Marry:
I'm so glad to answer your question,I have some good advice to you,I hope these suggestions can help you.
First of all,keep balance in food,have more vegetables and some meat.Mske sure you always have three or four meals a day.Eepscialy the breakfast,if you really don't have time,drink a cup of milk or juice before you go to school.
Second,do more exercise.It not only can make you more healthy but also good for you study.Choose one or two sports you like and keep on trying.
Last but not least,have enough sleep.As a student,sleep is very important for us,make sure you spend at least 8 hours on sleeping.
Congratulate beforehand you will be more healthy!
Yours Linda