The retrospective facilitator (often the scrum master) should have a toolbox of retrospective exercises, and be able to pick the most effective one.
This presentation explains the “why” and “what” of retrospectives and the business value and benefits that they can bring, and shows several exercises that you can use to facilitate retrospectives, supported with advice for introducing and improving retrospectives.
Retrospectives are a great way for teams to improve their way of working, to become more agile and lean. Getting actions out of a retrospective that are doable, and getting them done helps teams to learn and improve continuously.