Retrospectives is one of the most straight forward inspect-and-adapt cycles - most often, everyone just gets it. Still, as a facilitator (Scrum Master perhaps), preparation can really make a difference.
Here are some resources for preparing a retro.
Books
Project Retrospectives: A Handbook for Team Reviews (Dorset House eBooks) by Norman Kerth Link: http://a.co/2UADhR2
Agile Retrospectives: Making Good Teams Great (Pragmatic Programmers) by Esther Derby, Diana Larsen Link: http://a.co/9HFOL1D
Fifty Quick Ideas To Improve Your Retrospectives by Tom Roden, Ben Williams, Nikola Korac Link: http://a.co/dsC5Qo2