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.
Template:
Address.
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.
Yours lovingly,
Name and signature.