Friends often share things via letters and those friendly letters has some important things to cover. A friendly letter template is shown below where you can find how one friend writes a friendly letter to another. You can also follow this kind of template for writing friendly letters. You can write anything you like to share with your friend.
Date of letter.
Dear name of friend,
I hope you are fine with your health Jesica. How are you and your parents? Convey my regards to everyone in your family.
I am writing this letter to inform you that I will visit California next week for a conference. As I will be free on the weekends, I want to meet you all, since we met long ago. Tell me your convenience, so that we can plan our meeting effectively.
Name and signature.