Go backstage.
If all the world’s a stage, there’s got to be a lot of stuff hidden behind the scenes. Walk backstage after a show. Walk backstage anywhere. Talk to the people you find there. Trespass mildly. Open doors that interest you, even if they say “STAFF ONLY: WRITERS KEEP OUT.” Simply open them and walk through. At worst, someone will notice and ask you to leave (apologize and/or play dumb as needed, remembering these magic words that always work for me: “Sorry, I was just looking for the bathroom”). You’ll still catch a glimpse of something you haven’t seen before.
Cops essentially live backstage, know what I mean? Talk to them. The first time I nervously walked up to a police officer with an off-the-wall question, I was curious about why there were so many people begging for money on the main drag in Berkeley, Calif. I got a respectful, long answer that sparked a deeper interest in street people. That interest led me to write realistic passages about street life in my novels Lucky Stiff, Easy Street and The Extra. Now I talk to cops all the time.