Get involved in the dream plot, and forget about the fact that you're dreaming. Sometimes, even if you try to keep yourself focused on the fact that you're dreaming, you can end up becoming non-lucid. So if you don't think about the notion that you're in a dream, that just makes it easier to lose your lucidity.

Passive dream control also makes it easier to become non-lucid (passive control is not commanding the dream to do something or shouting out an action; instead, it simply involves you "knowing" that something will happen, as if you're acting out a role in a movie).

Surely you wouldn't want to lose lucidity, though?