We learn by comparing our behavior to others.
What options do you offer people on your site to compare their behavior to other visitors? Show them how others interact with your website and/or products through twitter/ facebook/ comments/ a forum. Show what the most popular products or searches are ('people who looked at eventually bought product X'). You can also highlight or reward people who demonstrate positive interactions with your site ('customer of the month' or a list with 'most active commenters').
Further reading on Mimicry at the Wheel of Persuasion.