By Ann Grove, President of Logical
What are user stories, you may ask? A user story is a written tool to describe in narrative form how a user expects to interact with software.
Wikipedia explains it this way: "In software development and product management, a user story is one or more sentences in the everyday or business language of the end user or user of a system that captures what a user does or needs to do as part of his or her job function. User stories are used with Agile software development methodologies as the basis for defining the functions a business system must provide, and to facilitate requirements management."
Making user stories both simple and meaningful to the software development process requires more effort than producing low-value user stories that are lengthy and excessively complex.
I think Tarun Kohli, who founded Quovantis, a boutique services company in India, does a great job of explaining the The Art of Making User Stories. Even if this approach doesn't fit your needs, it is a great place to start to ensure proper focus.