Pawnstorm has a good article up entitled “Depth” with useful tidbits like:

“First off, know your worlds well. The better you know the backdrop the more effectively you will be able to drop references. Second, make random references. There is no rule that says everything has to be explained, chances are, if its really interesting, readers will come up with an explanation on their own. Third, make sure that everyone has more than one motivation. Think about it, everyone in real life is acting upon multiple motivations (some of them conflicting) at any given time, you characters should be no different, although this will require you to think about what their environment is more than you might otherwise.”

Good advice. I would add, create a quadrant visual to polarize your characters against each other, but against each other’s motivations at least four ways. It’s like ready-bake irony. — Ways to amuse yourself on those tenth version edits.