Explain the problem. First of all, you should write your complaint in details, and in good language.Find out how to craft a formal complaint letter. Learn about key components, structure, and tips for an effective complaint. Be clear and concise. Describe the item or service you bought and the problem. We will explore the key elements of a complaint letter, provide writing tips, and offer a sample letter to guide you in effectively addressing your concerns. Draft your letter on both e mail and your word processing program. Handling customer complaints requires a careful, delicate approach. You should indicate your reasons for writing the letter.