Where Do Large Groups of People Gather?
Keep up to date with the calendar of events in your area or cities nearby. Are there any special events where large groups of people are expected to gather? Perhaps a hot air balloon event or wine tasting event? Any art or craft fairs or garden shows? Take a look at http://eventguide.com for events in major cities. Car shows? Horse shows? Outdoor concerts? What do all of these have in common? They all attract a large number of people with similar interests. Go to some of these events, have fun and try to come up with some book ideas that could be sold to this audience.