When you write a letter to a friend, the letter can be relaxed and casual. However, when you type up a professional letter, called a business letter, there are certain guidelines that you need to follow. It is completely acceptable to type a warm, friendly correspondence to a business associate with whom you have an affable relationship. The key to writing a successful letter is to follow the proper format, which is explained in the following steps.

Begin With Yourself

Start the letter with an address block showing your return address. If you are typing the letter onto letterhead, this step is not necessary, provided the letterhead shows your full name and return address. Skip a line.

Give It a Date

Enter a line showing the date of the letter. The date format should be either month, day and year or date, month and year. You should spell out the month, no matter which format you choose. It is acceptable to include the day of the week, but not necessary. Skip a line.

Name the Recipient

Type in the recipient's information in an address block. Type her full name, including title such as "Ms." or "Dr.", on one line. On the next line, type in the street address. Type the city, state and zip code on the final line.

Use a Salutation

Skip a line and enter the salutation. Professional letters should always be addressed "Dear Mr./Ms./Dr./etc." followed by the recipient's last name. Follow the name with a colon. If you do not know the name of the recipient, address the letter with a general yet professional salutation, such as "To Whom It May Concern," or "Dear Sir or Madam."

Write the Body

Enter another blank line and type the body of the letter. You do not need to indent the first lines of paragraphs in professional letters. Keep the letter concise, typing no more than three or four paragraphs. Type double spaces between each paragraph.

Close the Letter

Skip a line following the final paragraph. Enter a closing line, such as "Sincerely," or "Yours Truly." Enter four blank lines and then type your full name. Type your title on the line after your name, if applicable. When you are done typing and printing the letter, sign your name in the space between the closure and your name.