Where do you find your ideas?

Linda Newbery and Nicola Davies answer this question in this article, From Idea to Story.  Here's a quote:

"Where do you get your ideas from?" Every author who gives talks to children or adults has been asked this question hundreds of times, and of course there's no simple answer. Ideas are everywhere - the trick is to recognise a promising one when you get it, and not let go. Your starting point may be something that's happened to you, or to someone you know; a news item; a fear, or a dream; something from the past; a fascinating character; a painting or poem; and of course our heads are crammed full of ideas and images from books we've read, stories we've heard and films we've seen.

When a promising idea grabs hold of you, hang on to it and see if you can turn it into a story, or at least the beginning of a story. You can build on it by asking yourself questions and thinking of the answers. Who? When? Why? will get you started; then more and more questions will follow: But why doesn't he tell anyone? Who could possibly help her? Where have his parents gone? What's he hiding from? At this stage, it's a game: you haven't committed yourself to anything, and can enjoy playing around with ideas and possibilities.

Playing around with ideas and possibilities, and pursuing good ideas.  A very good place to start...