How To Write An Informal Letter Lesson Plan . After the lecture the students will then get into there groups, of four, and work on there letters. Write a friendly letter with appropriate components Informal (Friendly) Letter ESL worksheet by pirchy from www.eslprintables.com Just a short one week letter writing plan. This is a free sample so learning resources and powerpoints are not included, follow the link below to access the full lesson. C) understand what an order letter is.