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.
Introduce SMART goals (specific, measurable, attainable, relevant, timely) and examples for SMART vs not so smart goals, e.g.'We'll study stories before pulling them by talking about them with the product owner each Wednesday at 9am' vs. 'We'll get to know the stories before they are in our sprint backlog'. Form groups around the issues the team wants to work on. Each group identifies 1-5 concrete steps to reach the goal. Let each group present their results. All participants should agree on the 'SMART-ness' of the goals. Refine and confirm.
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.