Format your letter by writing your address on in the top right corner of the page, and the recipient's address on the left side of the page, on the line just below where your address ends.
Add the date or either side of the page, including the entire month, not just an abbreviation. The salutation should be "Dear Mrs." or "Dear Dr." in keeping with the formal nature of the letter. If your letter is not addressed to a specific person, "Sir," "Madam" or "To Whom it May Concern" are also acceptable.
Compose the body of the letter. Begin with a short introduction of the topic you wish to discuss and then go into more detail in the later paragraphs. The final paragraph is the action paragraph. It should detail your suggestions for solving whatever issues were posed in the body of your letter.
Use good grammar and punctuation. For a formal letter, first person is acceptable to denote something the writer thinks or plans to do. "We" may be used to commit the company the writer works for to the actions outlined in the letter. Use active voice as much as possible to keep the writing focused. Writing "Mary mailed the letter" is more appropriate than "The letter was mailed by Mary." Use this structure as much as possible in your formal writing.
Conclude the letter with an appropriate closing. "Sincerely," "Yours truly," or "Yours faithfully" are viable options. Place your name just below the closing.