Set up a 'retrospective mailbox' at the beginning of the iteration. Whenever something significant happens or someone has an idea for improvement, they write it down and 'post' it. (Alternatively the 'mailbox' can be a visible place. This can spark discussion during the iteration.) Go through the notes and discuss them. A mailbox is great for long iterations and forgetful teams.
Split a large group into smaller ones that create posters Source:
Unknown, adapted by Corinna Baldauf, inspired by Michal Grzeskowiak
After you've identified an important topic in the previous phase you can now go into detail. Have the larger group split up into groups of 2-4 people that will each prepare a poster (flip chart) to present to the other groups. If you have identified more than one main topic, let the team members select on which they want to work further. Give the teams guidelines about what the posters should cover / answer, such as:
What exactly happens? Why is that a problem?
Why / when / how does this situation happen?
Who benefits from the current situation? What is the benefit?
Possible solutions (with Pros and Cons)
Who could help change the situation?
... whatever is appropriate in your setting ...
The groups have 15-20 minutes to discuss and create their posters. Afterwards gather and each group gets 2 minutes to present their results.
Condense many possible actions down to just two the team will try Source:
Lydia Grawunder & Sebastian Nachtigall
Hand out index cards and markers. Tell everyone to write down the two actions they want to try next iteration - as concretely as possible (SMART). Then everyone pairs up with their neighbor and both together must merge their actions into a single list with two actions. The pairs form groups of 4. Then 8. Now collect every group's two action items and have a vote on the final two.