Next time you are sizing a large number of stories - especially when beginning a new project - consider using a visual method. This exercise is best done with a long table. Begin with an average size story card and place it in the center of the table. Take the next story and place it either above or below the first story depending on its size. The team should, one at a time, place stories on the table relative to the size of those already laid out. Rather than trying to define an absolute size, the team will sort stories based on their approximate size.
This exercise forces people to think in relative terms instead of absolute estimates. Once all the stories have been placed in order, the team takes a set of planning poker cards and inserts each card along the spectrum of stories to identify the transition from one size to the next larger one. For example, those stories on the simple end of the sizing spectrum will start at "1", and the team will place the "3" card at the point where the first story is that should be sized as 3 instead of 1. The team is done once they have ordered every story on the table and grouped them into one of the story sizes.
This visual exercise is most useful when a team has a hard time moving from the high precision exercise of estimating to the relative exercise of sizing. It is also useful when there are a large number of stories to be sized, as most teams will move through the sizing much faster than in traditional planning poker. However, it does allow each individual to provide an unbiased opinion, and moderators should be sensitive to the fact that soft spoken team members may have a harder time offering input.
If anyone tries this, let us know.