I listened to Craig English, a teacher and author at the PNWA conference about how he creates urban fantasy. He said urban fantasy is something freakish or a personal moment of otherness that happens to a character. The character might not embrace the strangeness at first, depending on their background, turmoil, and religious preference. Then up the stakes after the odd episode and see how the character deals with it. It could be a flexibility of reality. Establish the mundane world, then the fantasy, and balance the two. Decide on a theme and the rules of the weird. The character realizes the world is not quite what it seems.