Vonnegut's rules for writing short fiction, lifted from BoingBoing.net, lifted from his book Bagombo Snuff Box:
1. Use the time of a total stranger in such a way that he or she will not feel the time was wasted.
2. Give the reader at least one character he or she can root for.
3. Every character should want something, even if it is only a glass of water.
4. Every sentence must do one of two things -- reveal character or advance the action.*
5. Start as close to the end as possible.