How do you choose what you dream about?

Dreams are, by their nature, involuntary, because they are a function of the unconscious mind. One cannot choose what one dreams of. Even in the current hype about lucid dreaming, one only becomes aware that a dream is in progress, and then attempts to direct that dream. Some individuals learn to "incubate" a dream by meditating and focusing on a specific topic before falling asleep. But even this skill only provides a vague direction for a dream. One cannot choose a topic before the dream occurs, as one might choose a video or television show.