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.
What would make the next iteration a perfect 10 out of 10? Source:
Prepare a flip chart with 2 columns, a slim one for 'Rating' and a wide one for 'Actions'. Everyone rates the last iteration on a scale from 1 to 10. Then they have to suggest what action(s) would make the next iteration a perfect 10.
Collect what to start, stop, continue, do more and less of Source:
Draw 5 spokes on a flip chart paper, dividing it into 5 segments. Label them 'Start', 'Stop', 'Continue', 'Do More' and 'Do less'. Participants write their proposals on sticky notes and put them in the appropriate segment. After clustering stickies that capture the same idea, dot vote on which suggestions to try.
Prepare 3 flip chart papers titled 'Helped', 'Hindered', and 'Hypothesis' (suggestions for things to try out). Ask participants to help you grow and improve as a facilitator by writing you sticky notes and signing their initials so that you may ask questions later.