According to Purdue University’s Online Writing Lab, business letters take one of three formats: block, modified block and semi-block. In block format, the business letter is left justified and single-spaced with double spaces between paragraphs. The modified block format calls for the addresses and the letter’s body to be left justified, while the date and closing are centered. Semi-block follows modified block except that paragraphs are indented.
Business letters should have 1-inch margins on all sides. Regardless of a business letter’s format, the font should be easy on the eyes. Times New Roman in 12 point is common, as is Arial; many companies prefer a sans-serif font to give a more modern appearance. Colons should be used after salutations and commas used after closings.
The general form of business letters takes a standard layout: sender’s address as letterhead or in the letterhead space, date, recipient’s address, salutation, body of the letter, closing, and finally notification of any enclosures.
When writing out the appropriate closing statement, which must match the salutation used, only the first word (such as the "Yours" in "Yours truly") should be capitalized. The letter writer should leave four blank lines between the closing and the printed name to provide space for a personal signature.