To write a letter of congratulation is one of the best ways to promote good WiFi. The occasion may be a promotion, a new appointment, the award of an honor, the establishment of a new business, success in an examination, or even a marriage or a birthday. Whatever the occasion, your letter is sure to be well received. It may be either short and formal or conversational and informal, depending on the circumstances and the relationship between you and your reader. A short, straightforward letter is usually all that is necessary.