Set the formatting in your word processing program to left-justified, single-spaced.
Type your return address on the first two lines, spelling out words like "street" and "avenue." (State abbreviations are fine.)
Skip a line then type the date, spelling out the month.
Skip a line and type the name, company and address of the letter's intended recipient including titles like "Ms." or "Dr.," which can be abbreviated. Again, do not abbreviate words like "street" or "avenue."
Skip a line then type the salutation, punctuated with a colon. For example, "Dear Dr. Edwards:" (type this without the quotation marks).
Skip a line and write a brief summary of the letter's purpose, such as "Invoicing Procedures for ABC Project" without ending punctuation. Center and bold this line.
Skip a line and readjust formatting to left-justified. Write the body of your letter, skipping a line between each paragraph.
Create your signature block. A closing such as "Yours faithfully," "Respectfully yours" or "Sincerely yours," are all professional and appropriate. Skip four lines and type your name, then your title and company directly below.
Skip two lines and type "Enclosures" and the number of pages you are including in parenthesis. You may omit this step if there are no enclosures or attachments.
Print the letter. Sign it in the space between the closing and your typed name.