The town hall format has some significant advantages and disadvantages for Trump. It is unlikely that the citizen questioners will be given the right to cross-examine him, and fact checking will be harder; that will help him. On the other hand, the candidates will be expected to show some empathy for the questioners, and Trump is incapable of doing that, because, in his eyes, everything is about him.
My advice to Clinton is simple: only make personal attacks as counterpunches; go high wherever possible; don’t rely on the moderators to do any fact checking; be clear and firm when you’re on defense; and let him hang himself.