The goal of the retrospective is to talk through what went well, what went wrong, and what can be improved.
All retrospectives should have an impartial moderator. This moderator actively attempts to remain objective and is focused on guiding the conversation forward throughout the meeting.
<aside> <img src="/icons/warning_yellow.svg" alt="/icons/warning_yellow.svg" width="40px" /> If the moderator doesn't guide the conversation successfully, the retrospective could be dominated by a few "loud voices" or could stay focused on the facts and feelings about the past iteration without drawing any conclusions.
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Emotions are not only allowed in retrospectives, but they should also be encouraged. Emotional language ("I was angry when…," "It made me sad that…") not only helps convey intensity, it also helps expose issues that may have been difficult to sort out otherwise.
When possible, all parties should be present. No one should have to worry about sharing concerns or experiences because another party isn't there to represent their side of the story.
When necessary, get people face to face. After a particularly difficult iteration, or when there's a strong risk that emotions will be running high, it's almost always worth the cost to have everyone in a video meeting to talk through the retrospective in real-time.
Remind people of the purpose of the retrospective, and that the conversation should be scoped to the project/iteration under review. Ensure everyone understands the rest of the agenda.
The moderator reviews the improvements the team identified in the last retrospective and discuss progress on those items.
Don't try to draw any conclusions up front, simply collect facts. This can be done by constructing a timeline, soliciting impressions ("what made you mad, sad, or glad in this iteration?," etc.), or any other number of fact collecting exercises.
Work together to identify patterns or causal relationships (because we did x, y happened).
With the insights firmly in hand, it should be fairly easy to identify action items for the group. Consider having group members vote on which things are most important to be acted upon.