To whet your appetite and keep your writing fingers limber, take a good look at the photo, or let a prompt settle in your mind. Set a timer for a reasonable amount of time, be that five, fifteen, or thirty minutes. Then start writing.
Your character receives a strange letter directing her to do something she would never consider doing. Except that she must.
Describe a letter you wrote or received that made a difference in your life.
Write an article in the form of a missive that explains why people should revive the art of letter writing.