Find a public space or place where there are lots of people and hang out. Observe how people interact with each other. Take a pic, jot down your observations then publish them online. Instagram and Twitter works well for quick stuff.
By publishing your pics, you're letting people know what's happening in the urban environment and helping to facilitate a dialog about the place. To maximize that interaction hashtag # photos with the neighborhood name or geotag the location that way other people can see what's happening in that place too.
Over time, your documentation will add up to a visual portfolio of city life. The pics are clues that capture what you were doing, when, and with whom. They tie us to the emotional and social aspects of place and time. When it comes time to solve problems in the city, all those clues, from all those documenters, make an amazing collective resource about the place.
Tweet your #CityLifeObservations to @patrickm02L on Twitter.