1) The document provides guidance on writing different types of letters, including social, business, and request letters. 2) It discusses the key components of letters, including address, salutation, body, and subscription. For social letters, it recommends a warm and personal tone. 3) For business letters, it advises being brief, clear and avoiding sentimentality in order to prioritize efficiency in communication between companies. The appropriate salutations in business letters are "Dear Sir" or "Dear Sirs".