Begin with a Rough Sketch

"Fiction begins with a rough sketch. One gets down the characters and their behavior any way one can, knowing the sentences will have to be revised, knowing the characters' actions may change... All that matters is, going over and over the sketch as if one had all eternity for finishing one's story, one improves now this sentence, now that, noticing what changes the new sentences urge, and in the process one gets the characters and their behavior clearer in one's head, gradually discovering the deeper implications of the characters' problems and hopes. Fiction does not spring into the world full grown like Athena. It is the process of writing and rewriting that makes a fiction profound and original. One cannot judge in advance whether or not the idea of the story is worthwhile because until one has finished writing the story one does not know for sure what the idea is."

~ John Gardner (On Becoming a Novelist, The Art of Fiction)