Letter of thanks to someone for doing something thoughtful:
12, XYZ Road,
New York,
USA
5, June, 200*

Dear Ron
I would like to convey my sincere thanks to you for your recent thoughtfulness. It was so kind of you to speak favorably about me to my chief. It was just what I needed buy never expected you always seem to know the perfect time to say or do. I am truly touched by your generosity, your spirit and willingness to go out of your way to help me. You are my real friend. I am indeed lucky to have a friend like you in my life. Thank you again for being so thoughtful.

Sincerely yours
John