Answer:
Wear a watch throughout the day and constantly look at it. Your dreams are, fundamentally, your mind processing the events that happened the previous day. Therefore, if you look at your watch periodically, you will do so in your dream. Dreams cannot comprehend what exact time it is, so when you look at your watch in the dream, you won't see what the precise time is. Therefore, you will realize you're dreaming, or lucid dreaming. From there on out, you may control your dreams.