Set up a 'retrospective mailbox' at the beginning of the iteration. Whenever something significant happens or someone has an idea for improvement, they write it down and 'post' it. (Alternatively the 'mailbox' can be a visible place. This can spark discussion during the iteration.) Go through the notes and discuss them. A mailbox is great for long iterations and forgetful teams.
Hand out pens and sticky notes. Ask everyone for ideas on how to turn the next iteration / release into a certain desaster - one idea per note. When everyone's finished writing, hang up all stickies and walk through them. Identify and discuss themes. In the next phase turn these negative actions into their opposite.
Introduce SMART goals (specific, measurable, attainable, relevant, timely) and examples for SMART vs not so smart goals, e.g.'We'll study stories before pulling them by talking about them with the product owner each Wednesday at 9am' vs. 'We'll get to know the stories before they are in our sprint backlog'. Form groups around the issues the team wants to work on. Each group identifies 1-5 concrete steps to reach the goal. Let each group present their results. All participants should agree on the 'SMART-ness' of the goals. Refine and confirm.