How to Write a Friendly Letter. When writing a letter to a friend or a friendly acquaintance it's important to use the right style and tone to give the letter a feeling of casual but sincere friendliness. Also, a friendly letter should be written in the proper format so that informal sentences aren't jammed into a highly formal style.

Start with a heading. A heading is a functional part of the letter that lets the recipient know on which date the letter was written and from where it is coming. Start on the upper right hand side of the page. Put your own address first, indented to the middle of the page and aligned to the right. Underneath your address put the date of writing.

Open with a greeting. Your greeting can be almost anything you want, depending on the nature of your relationship with the letter's recipient. The most standard greeting for a friendly letter is "Dear" followed by the person's first name and then a comma. Put the greeting two lines below the heading and align it flush-left.

Write the body. The body of your friendly letter can include anything you want, so long as the tone is in keeping with the rest of the letter and your relationship. Use paragraphs to separate significantly different ideas and indent the first sentence of each paragraph by about five spaces.

Add a closing. Just because your letter is friendly one doesn't mean that you should just end it abruptly. Use a closing, otherwise known as a complimentary line, at the end of the letter. The most common closing is "Sincerely"; however people use all kinds of closings such as "Yours," or even "Waiting for your response." Place the closing two lines beneath the last sentence of the letter and place a comma after the closing phrase or sentence.

Sign the letter. You should sign the letter about two or three lines below the closing line. You can use a pen to sign the letter, or if you're working on a computer or typewriter you can just type in your name.