User story maps are a very good way of eliciting what needs to be done to get a feature/product done, done. The article below explains how user story maps can be created. The author recommends that this be done with a small group of people, as a larger group can slow things down a bit. From personal experience, I have done this with a larger group, so that we get a good representation from both business people, and those more closer to the technology stack.
The diagram in the article is a good visual representation of how the map is formed, but we took it one step further and used personas in the mix. This allowed us to understand what our MVP might be, but also, work on the part of the map that would affect the main, or most of the users first. This worked in our favour, as we were working on the more riskier items first, and allowed us as a team to focus our efforts on satisfying more of our customers, sooner.
A link to the article is here: http://winnipegagilist.blogspot.co.uk/2012/03/how-to-create-user-story-map.html