Some damned good fiction advice from Teresa Nielsen Hayden, just back from teaching the Viable Paradise science fiction/fantasy writing workshop on Martha's Vineyard. Rules 3 and 4 are particularly nice stuff, just the sort of thing I find myself paying attention to as I work on the sequel to Little Brother:
3. Recycle your characters. Give preference to characters already used in earlier episodes, or to characters connected with them, when you're peopling later events. Characters are made more interesting by being reused, and it increases the overall consequentiality of the story. One-time single-purpose characters are occasionally necessary, but they don't support as much weight.
Cherish your good secondary characters. They're infinitely useful.
4. See if you already have one. Whenever you need something new — prop, plot thread, setting, minor character — go back through the parts of the story you've already written and see whether you can find it there. It's surprising how often the exact thing you need is already sitting there in plain sight.