Give positive, as well as non-threatening, constructive feedback Source: Inspired by Satu Rekonen
Hang up two flip charts, one headed 'I like' and the other 'I wish'. Give the participants 5-10 minutes to silently write down what they liked about the past iteration and the team and what they wish was different (and how it should be different) – one point per sticky note. When everyone is finished, go around the circle and everybody reads out their 'I like' items and hangs them up. Repeat the same for the 'I wish' stickies. Either debrief or use the stickies as input for the next phase.
Prepare a flip chart with 3 columns titled 'What', 'Who', and 'Due'. Ask one participant after the other, what they want to do to advance the team. Write down the task, agree on a 'done by'-date and let them sign their name. If someone suggests an action for the whole team, the proposer needs to get buy-in (and signatures) from the others.
Let team members appreciate each other and end positively Source: Agile Retrospectives who took it from 'The Satir Model: Family Therapy and Beyond'
Start by giving a sincere appreciation of one of the participants. It can be anything they contributed: help to the team or you, a solved problem, ...Then invite others and wait for someone to work up the nerve. Close, when no one has talked for a minute.