There's this book called "Dream While Awake:Techniques for 24-Hour Lucid Dreaming."

It talks about noticing your dreaming mind while in a waking state. (Yes, it's operating in the background) When you get associated to the subtle cues of this "daydreaming" you are more able to predict and notice when you're sleep dreaming. It expands way further than just sleep dreaming, which happens only when you sleep. That's why I find this interesting, because you have more choices for improving Lucid Dreaming while being awake. Also, it makes you more susceptible to Lucid Dreams, of course.