Effective letter writing boils down to knowing why you are writing a letter, understanding your reader's needs and then clearly writing what you need to say. Every letter should be clear, human, helpful and as friendly as the topic allows. The best letters have a conversational tone and read as if you were talking to your reader. In brief then, discover the Seven-Cs of letter writing. You should be
When you write a letter, you are trying to convince someone to act or react in a positive way. Your reader will respond quickly only if your meaning is crystal clear.
Put yourself in the reader’s shoes and write in a friendly and helpful tone. Don't represent your company as one that cannot make a mistake and must always be in the right. Try not to reply in the normal bland and defensive way of organizations—write a sincere and helpful letter.
Show you are interested in the reader’s circumstances. If he or she has mentioned something personal in the letter, refer to it in your reply. This builds a bridge between you and the reader. Read the original letter carefully and see if there is something you can put in your letter to show your interest.