Regularly the team reflects on how they worked during the last period, what went well, what could be improved, and selects one or two improvement axis.
There are many ways to run a retrospective.
Let's quote some of them: starfish & Niko Niko
Starfish practice is coming from Agile principles.
Sea Star diagram: https://www.sessionlab.com/methods/starfish
Brainstorming session with post-its on what the team should DO MORE, DO LESS, START DOING, STOP DOING and KEEP DOING.
Ideas are clustered and then the team votes for the best ideas. They keep one or two improvement ideas.
Niko, niko: it is a mood graph where each members draw his/her mood during the period and then explains variations, peeks. The team can then decide what to improve to increase their good mood.
Prepare axis on a board (horizontal representing time, and vertical one representing the mood - could be positive and negative). Each participant draw their mood graph during the period and then give explanations