Keep a Constant - Theory about dream control
So if anyone doesn't know, in math, a constant is a number that doesn't change. This rule also applies in theory's time travel, with a physical constant. For example, when a subject time travel's, they need a Constant, something that exists in both time periods. (This is all derived from different scientific theory's of physics).
But to apply it in lucid dreaming is simple. One might conclude that a constant (basically anything you want) can be something found both in your real world and your lucid world. This would theoretically strengthen the experience and keep the dream in line.
Another might conclude that a constant should be something you keep with you all through your lucid dream, and future lucid dreams you have. Again, keeping your dream in-tact.
This is just a theory I came up with, never tested it. I rarely go lucid so I can't totally vouch for this. If you want a clearer picture of this, just watch Lost, episode 5.05, The Constant.