Being able to lucid dream requires that you be fully self-aware and undistracted by thoughts that relate to your waking life. While you are laying in bed trying to fall asleep, clear your head of distracting thoughts, and focus all of your attention on the fact that you are falling asleep and about to enter a dream state. Meditation will also help you clear your mind of all of the negativity that will keep you from having a restful sleep. Before you go to bed, decide what you want to dream about. Paint a vivid image of your surroundings, and be sure to include details like sights, sounds, and smells. Put yourself in the scene, and try moving around within it.  Pay attention to the sensations of breathing and walking around in this dreamscape. Though you are not yet dreaming, tell yourself "I'm in a dream." Continue this visualization technique until you have fallen asleep. Choose your ideal location for optimal results. Leave a photo, a symbol, or even a blank piece of paper at your bedside before you fall into sleep. Take something that represents the thing you want to dream about and leave it out before you go to bed so that it can help you transition into the dream you want to have. If you want to dream about a certain person, have that person's picture out near you. If you're an artist who is struggling to find a subject, leave a blank canvas at your bedside.  Taking this measure can prime you to dream about the things you want to dream about because it will plant the kernel of these things in your mind before you go to sleep. As you lie in bed and get ready for sleep, tell yourself something as simple as, "Tonight, when I dream, I want to realize I'm dreaming." Repeat this to yourself a few times and really focus on making it happen. This will help you get in the mindset you need to be in to recognize that you're dreaming. If you really want to control your dreams, then you should sleep in complete darkness, or as close to complete darkness as you can. Sleeping in darkness keeps your melatonin levels...

TL;DR in Chinese:
睡前冥想。 在脑中展示你的梦境。 在床头摆上梦中需要的场景的照片、标志、或者一张白纸也好。 睡前不断暗示自己要控制梦境。 关灯睡觉。 尝试清晰梦境记忆归纳法（MILD）。 赶走噩梦。