Writers are nosy; they don't mind their own business. They eavesdrop. They spy. In Seattle there is a bus I once rode. Stuff happened on that route. A couple sat handcuffed together. A man got on and poured his coffee in the coin box when asked to dump it outside. A guy on a cell was trying to buy a goat. A dog got on without any apparent owner and got off two stops later.
I listen in on conversations and try to capture patterns of speech. No character speaks the same as another character. I write down snatches of what I hear. A person's speech tells us a lot about his education, where he grew up, about his job, his self-esteem. The volume of pitch of spoken words vary during conversations. I listen secretly.
Sometimes I sit in a public place near the most interesting people I can find. Get myself a coffee and open my notebook. I'm unobtrusive, but I listen. I don't even have to see the people talking. Later I will put these people in a complication. They can be in a very ordinary situation such as washing the supper dishes or talking during an opera intermission. Trouble finds them when they least expect it. They're surprised when during a perfectly routine event becomes potentially difficult.
I listen wherever I am. What I am waiting for are voices that evoke the human condition.