Here are some principles that congratulatory letters follow：
1. The purpose of writing the letter is to make your reader feel certain that he or she deserves the special message of recognition and praise.
2. The note should be brief, dealing with the primary topic only. These messages are most effective when they conduct no business.
3. The whole message should carry a tone of being positive and conversational.
4. Be sure to send the letter within a few days of the event. Any delay in delivery of the message would make your effort worse than no effort at all.