This is my thing -- I always want to hear about any person's area of passion or expertise. It's usually much more interesting than small talk.

But I find it's often quite easy to get people started. I like to ask people about their work. (Scientists and engineers often seem particularly willing to talk, but there's certainly a range.) If someone mentions a hobby, I'll ask for details. I've learned a lot about ballroom dancing, guns, and violin from letting people ramble. It all comes down to being open to hearing long stories. I think people can somehow detect a willing listener, and as a result people seem to love to come to me with their stories.