you can write about personal or casual topics. informal letter You can catch up with a friend, update them on your life, make plans, express your feelings, share news, or ask for advice. The tone of the letter should be friendly and conversational. Start with a greeting, and use the recipient's name. You can be more relaxed in your writing and use contractions. End the letter with a closing and your signature. Remember to keep the letter brief and to the point, focusing on one or two main ideas. Also, be sincere and avoid anything that may be offensive or hurtful.