Recently I tried writing a piece of 'flash fiction.' It was an interesting exercise, to tell a story in just 250 words. Obviously there can't be much of a plot, or an in-depth study of character. So you are more or less forced to rapidly set up a situation and then provide some sort of denouement.
What I found was that this could work as a method of planning a longer story. While I was producing that flash fiction I found myself speculating about the context, the characters. It could be a useful way to kick-start your imagination if you are short of ideas.