The basic structure of a formal letter: The rules might be arbitrary, but taken together they create a formula that produces clarity. When a letter follows all the rules, the reader doesn’t have to struggle to figure out where a piece of information might be, what action they should take next, or who sent it _ everything can be found in its place. Knowing the rules of letter writing is, in that sense, akin to knowing the rules of page layout or web design _ the format of the document should support and clarify the content.
I can’t tell you how many truly awful letters I’ve had to read in my life. As a former administrative assistant, I was responsible for all the unsolicited submissions to a major New York museum. Artists and collectors all over the country (and abroad) wrote to have their work considered for display or acquisition, and to be honest the decision frequently rested more on the quality of their cover letter than on their work _ which, romantic dreams aside, rarely if ever sells itself.