One possible version:
Dear John,
I’m glad to hear that you are going to travel. Now I’d like to share my view on travelling with you.
In my opinion, travelling is a very good activity. When you get tired with your work or study and when you have free time, you can go out to enjoy the beauty of nature. You can breathe the fresh air, meet different people and make friends with them. Only by relaxing yourself will you forget your tiredness and build your health.
In order to have a pleasant journey, you need to make full preparations ahead of time. You’d better have clear information about the weather, and bring proper clothes, a camera, some medicine for common injuries and diseases and so on. On your journey, you must pay attention to what you eat. Be careful with everything everywhere in case your money gets stolen.
Do you agree with me? Wish you a good journey.
Yours，
Li Hua