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.
Asking and answering go around the team circle - an excellent way to reach consensus Source:
Everyone sits in a circle. Begin by stating that you'll go round asking questions to find out what you want to do as a group. You start by asking your neighbor the first question, e.g. 'What is the most important thing we should start in the next iteration?' Your neighbor answers and asks her neighbor a related question. Stop when consensus emerges or the time is up. Go around at least once, so that everybody is heard!
Let team members appreciate each other and end positively Source:
Agile Retrospectives who took it from 'The Satir Model: Family Therapy and Beyond'
Start by giving a sincere appreciation of one of the participants. It can be anything they contributed: help to the team or you, a solved problem, ...Then invite others and wait for someone to work up the nerve. Close, when no one has talked for a minute.