The most common style for a business letter is block format. Block format simply means that the whole letter is single spaced, save for a double space between each part of the letter and each paragraph, and is left-justified. For example, there is a double space between the sender's address and the date of the letter; there are only single spaces, however, between individual sentences within paragraphs.
Your address should either be on the letterhead of the paper; if you don't have letterhead, the sender's address starts on the first line on the top right side of the paper. The city, state and zip code go directly beneath on the second line. If it is an international letter, the country should be typed in all capital letters on the third line. If desired, you may add a phone number and email address after the mailing address.
The date is placed directly underneath the sender's address. Double space after the sender's address and write the full date in month, day, year format.
The recipient's address is placed directly beneath the date. Double space after the date and type the recipient's title and name on the first line, the street address on the second line, and the city, state and zip code on the third line. If it is an international letter, the country should be typed in all capital letters on the fourth line.
Double space after the recipient's address and use an acceptable formal greeting, such as "Mr.," "Mrs." or "Dr.," and the person's full name, followed by a colon. If you don't have a specific person to whom you are addressing the letter, use a general greeting such as "To Whom it May Concern."
Double space after your greeting and left-justify all of your paragraphs. Spaces between paragraphs within the body are always double spaced.
Double space after your last body paragraph and use an acceptable formal closing word or statement, such as "Sincerely" or "Regards." Space down four times and type the full name of the person signing the letter; these blank spaces leave room for a signature.
Double space after the typed name of the sender and, if you have any materials you are enclosing with your letter, type the word "Enclosures" and then indicate in parentheses how many enclosures you are sending with the letter. If you are sending a letter with no additional materials, you don't need this line.
If you are typing the letter for someone else, type your initials immediately below the "Enclosures" line. If you are typing the letter for yourself, you don't need any initials.