Learn how to write an informal letter in English with a casual and personal tone. Find out the format, structure and examples of informal letters to friends and family. Learn how to write an informal letter in English with proper format, structure, and examples. Explore types of informal letters—thank you, personal, invitation, and apology—with samples and topics to practice. Letter Writing in English. Check out what is a Letter, types of letters, tips to write good letters, solved examples of Letter writing in English. Tips to Master Informal Letter Writing To master writing informal letters in English, one must pay attention to several points, including the intent, vocabulary, tone, and structure of the letter.