Sprint Zero:
1. Sprint Zero should be used to create the basic skeleton and plumbing for the project so that future sprints can be truly add incremental value in an efficient way. It may involve some research spikes.
2. Minimal design up front is done in Sprint Zero so that emergent design is possible in future sprints. This includes putting together a flexible enough framework so that refactoring is easy.
3. For minimal design up front, the team picks up a very few critical stories and develops them to completion. Since these are the first few stories, delivering them includes putting the skeleton/framework in place, but even Sprint Zero delivers value.
Note: The velocity of Sprint Zero may be very low compared to that of other sprints.
