Each user story should INVEST

I - Independent The user story should be self-contained, in a way that there is no inherent dependency on another user story. N - Negotiable User stories, up until they are part of an iteration, can always be changed and rewritten. V - Valuable A user story must deliver value to the end user. E - Estimable You must always be able to estimate the size of a user story. S - Sized appropriately or Small User stories should not be so big as to become impossible to plan/task/prioritize with a certain level of certainty. T - Testable The user story or its related description must provide the necessary information to make test development possible.

Iteration 0 -> is foundational work that is performed prior to development starting.