The dream muscle
Dreaming is like a muscle, the more you exercise it the stronger it gets. I have been practicing lucid dreaming ever since first seeing the movie "Waking Life" (an excellent watch, if you haven't already seen it) probably 15 years ago. 15 years later I certainly cannot say by any means I have mastered lucid dreaming. I have however become very aware of many of my "dream indicators", and spotting these dream indicators as they happen very often for me now triggers becoming lucid. As much as I'd like to say that when I become lucid I can then truly control and shape the dream from that point, but even then it's not so simple. Part of being lucid is staying asleep, often becoming lucid snaps you right awake. The characters in your dream really do turn against you though, like in Inception (they really did nail it in that movie), as this is your own subconscious saying "hey hey, wait a minute, you're not supposed to be down here, get outta here". Every now and then I'll give one of the characters in my dream an interrogation and only once did I ever have one of them admit to me that yes I was in fact dreaming. Anyway, the whole thing is really fascinating. But the more you excercise this dream muscle, the stronger it gets, and the better you get at it. I don't know that anyone has ever truly mastered it.