Waldman has tips:
What town hall debates offer that other debates don't is a picture of the candidates among voters. If you connect well with those voters, it can be extremely persuasive, but if you fail at establishing that connection, it can be disastrous. Nothing illustrates this better than a moment I've mentioned before, the infamous "national debt" question from 1992. It not only provided a vivid contrast between George H.W. Bush and Bill Clinton, it also demonstrated as well as any moment has the added complexities of the town hall debate. Bush not only made the mistake of taking the woman's question (about how the national debt has personally affected the candidates) literally, he got defensive ("Are you suggesting that if somebody has means, that the national debt doesn't affect them?"), made a ham-handed attempt to tell a personal story ("I was in the Lomax AME church…"), and generally looked like he couldn't wait to move on. Clinton, on the other hand, got as close to the questioner as he could, locked eyes with her, and showed her how he felt her pain.
Serwer sees dangers for Obama:
[T]own hall debates aren't so much arguments as acting competitions. The nature of the town hall format carries substantial risk for a rusty incumbent president and a candidate with something to prove. Obama is both. Romney, by practicing his Clinton impression, may be better prepared this time around, too.