I treated this topic briefly on twitter and thought it might be helpful to explore it in a little more detail for those with debates coming up.
The most important thing to remember with debates, particularly for down ballot races, is that you're talking to the people in the newspaper the next day, not to the people in the audience.
Voters who show up for debates already know who they're voting for. Few show up to decide who they want to support.
Your undecided voters will read about the debate in the newspaper the next day, or hear a clip of the debate on the radio.
Knowing that, how should you prepare for your debate?
Focus on whatever your theme has been throughout you campaign. If your message has been that the incumbent only shows up to work once a week and spends the rest of his time golfing, make sure you mention that multiple times. The writers are going to focus on a consistent theme in their article (or a major gaffe).
Steer your answers back to your theme as often as possible. For example:
Question: Mr. Johnson, your opponent has claimed that you don't have the experience to be Mayor of our city. How do you respond to that?
Answer: Thank you for the question. My experience in [x, y, z] has fully prepared me to be the Mayor of our city. And my opponent - who played 200 rounds of golf last year and showed up to 15% of the council meetings - doesn't have the kind of experience voters are looking for. He doesn't even bother to show up for work. Simply getting elected doesn't give you the experience to do the job. You have to be on the job. And my opponent has failed at that.
As a post script (because I absolutely love this response), here's how you answer a terrible, irrelevant question from a journalist aimed at hurting your campaign: