Letters of encouragement should ideally be written by hand, with relatively informal content that tells the receiver how much others are thinking of him and believe in him. Overall, the tone of the letter should express the writer's appreciation for both what the recipient has achieved and who the recipient is as a person. This sincerity conveys the depth of friendship the writer has for the recipient.
The content of the letter should be positive, focusing on either what the recipient has accomplished or what he may yet accomplish in the future without directly or implicitly criticizing the recipient for any recent setbacks he may have experienced. If the writer is in a position to offer direct and practical assistance for the recipient, he should do so in the letter.
Such letters should be written quickly when a friend experiences such a setback. These letters offer encouragement when the recipient may be feeling depressed and give him a tangible item of inspiration that he can examine as often as he needs to. When the recipient moves forward and achieves a new goal he has set for himself, the writer can write a new letter that motivates the recipient into further achievements.