How do you write a letter to a friend convincing her to read a book?

You're not going to be able to make anyone read a book, but you can describe the things in the book that you think your friend would like. This would be a more casual letter, so you wouldn't have to do the formal headings or closings like in a business letter. Just start with "Dear ___" and put their name in the blank. Tell them all about the book you think they'd like to read, and close with "Love, ___" and your name.