How To Write A Forma Letter . Since a letter is a formal mode of communication, you’ll want to know how to write one that is professional. Following the subject line or greeting, write the body of your letter. Enquiry Letter Format, Sample and How To Write An Enquiry Letter? A from www.aplustopper.com Include the following details when crafting a professional letter: If you’re wondering how to begin a formal letter, the answer is very simple. Formal letters should have a brief and correct ‘subject’ matter quoted separately.