Help me to improve this letter for A+

I had to write an informal letter for English class and here is what I came up with. Tomorrow, in about 7~ hours that has to be on teachers desk. If there is any possible modifications, pleas let me know. Thank you.
Letter:
Dear James,

It’s been a long time since I last heard from you. I know that you’re going to take A level exam and you have to learn a lot, but I think you’re studying too much. I’m worrying about your health.

My advice is to plan your time: first of all you should learn only during the day and sleep at least 8 hours a day. Secondly you should have a time for a rest- you should spend it on long walks on the fresh air.

Don’t forget to eat health and full of vitamins food. Your dishes should contain many vegetables and fruits. If I were you, I’d eat a lot of chocolates and peanuts because they’re good for memory. It’s cold outside in North Pole, so take care of yourself and wear worm clothes.

Don’t worry I’m sure you will pass this exam; I’m going to keep my finger crossed for you. I can’t wait to hear how is your exam results so write as soon as you know!

Best wishes, ...