Topic ideas for a letter to a best friend include updates on the writer's life, memories they made together and qualities the writer appreciates about his friend. Including jokes, particularly inside jokes between the two, makes the card light-hearted.
A handwritten note shows the friend that the writer is thinking of him, which makes him feel appreciated. Letters are also one way to keep in touch if the sender and recipient are in different areas.
Details about the writer's life keep his friend informed, especially if the two haven't seen each other recently. Possible details to write about include the writer's personal life, career, education or hobbies.
Writing about memories between the two shows the recipient that the writer appreciates the friendship. Writing about a time when the recipient was supportive gives the writer an opportunity to thank his friend for the help.
The writer can include anything he appreciates about his friend. Ideas include personality traits, such as the friend's sense of humor or loyalty, or something the friend does well, such as baking cookies or listening to people.
If the writer has trouble thinking of what to write, he should ask himself what he likes about his friend. He should write his first draft on scratch paper and then write the final draft onto a card or stationery.