Eavesdropping. I do that a lot. It’s easy, fun, and good for getting those creative juices flowing. Also, when friends say something intriguing, I let them know that some day their story or clever word usage could end up in a book. Fictionalized of course, so that often they won’t recognize themselves. With strangers…. they’ll never know.
Observation. People watching is such a kick. Even more fun is making up stories about those you watch. Why are they behaving that way? Who are the people they are with? I’ll bet even non-writers do this.
TV, radio, music and the movies. I’ve been known to take a premise or a snippet of and run with it. The end results never look remotely like the show from which I drew my inspiration.
Magazines and newspapers. Tons of great stuff there. Especially those advice columns and the stories of personal triumphs over bad situations.
And of course, life itself. Something happens to me or a friend or relative, or a friend’s friend, and I get to thinking, What if?
I’m sure there are other ways of generating ideas. If you know of any that aren’t mentioned here, please share.