Here's one way to do iteration planning. It isn't the only one, but it has been used many times and works well. Perhaps you should try it until you work out a scheme of your own.
The team gathers around a whiteboard for the iteration plan. It often helps if someone acts as facilitator or director to keep things on track.
The customer stands at the whiteboard, writes the name of one story on the board, and describes what the story means. The team asks questions and the group discusses the story, until they're sure they get it, but no longer.
Then the team proceeds to brainstorm the tasks for that story, while it is fresh in mind, writing short names for the tasks on the whiteboard right under the story name. It might ...