Mindfulness is simple, but it's not easy. When I'm on my computer, I can forget to check in with myself for hours. Then, when I do, I may notice that my shoulders are all tense, or that I've been wasting time checking email when I need to get something more important done.
This somewhat over-used suggestion about "singing like no one is listening" and "dancing like no one is watching" is simply a poetic way to say, "seize the day," and there are many ways to do that. Want to know a secret? Sometimes I do burst into song. Are you ready to give it a try?