Dear (имя друга),
Thanks for your letter.I was happy to hear that you want to know about healthy lifestyle I will tell you about Healthy lifestyle.
I think, the most important thing in healthy lifestyle are healthy diet and sport. You should drink much water and eat fruits and vegetables. Fastfood and fizzy drinks are very unhelthy. Also you should do sports. Sport can keep your fit. You should have a good night sleep and reduce stress level. And don't forget about vitamins. I also think, that have fun is good for your life and health.
That's all for now. Write back and tell me interesting story.
Best wishes,
(ваше имя)