In How to Write One Song, Jeff Tweedy writes:
We’re able to form really complex stories off the top of our heads. Conversation comes from our subconscious–we search for language, tell stories, express ourselves in a way that’s organic. I think that’s the starting point for writing anything. If you’re able to express yourself as a human, you’re able to mine that ability to create other modes of expression, to mine that ability for songs. To me, that’s the best evidence that everyone can write a song. Maybe not everyone can make a chord progression, but everyone can make up a story.
Tweedy demonstrates this by relaying a particularly spirited conversation he recently had, marking in bold snippets from that conversation, lifting those portions, and then rearranging the pieces until they had the rhythm and feel of a song.
A pretty nifty writing exercise, if you ask me.