Reviewing the high-level requirements, including capabilities and external integration.
Establish the need
Firstly we seek to help establish the need for a solution by using a problem definition process; that looks at ensuring the requirements are aligned with the project and business goals. In the early stages we tend to group related and affinity tasks together: referring to these as 'epics'. Technical complexity (effort)
It is vital that we explore the technical complexity, limitations and other factors that may influence the required effort to implement the requirement. Lastly - priority matrix
A great exercise we like to run in our workshops is the priority matrix game; where by we challenge the business to first plot the requirements in the relevant quadrant and next up have them ensure they are placed in relative importance to each other. This has proved a highly effective way of helping clients agree on what requirements make into an MVP (minimum viable product)
With the right framework and chairperson workshops are often revealing and highly rewarding for participants.