Visualization can be an incredibly powerful way to manifest what we want in our lives. I have seen experienced this in my life in a variety of ways. When I used to run track in high school, I would picture myself winning the race, and then my body would follow the intention that my mind sent: and most of the time that vision would come to fruition. I did the same during labors of my two children. As my soccer coach used to say, the game (and this applies to many things) is 90% mental, 10% physical. If you believe, it will come. If you don't believe.. well you can guess the next part.
I think many of us do not realize the effects that the not believing part can have on manifesting what we don't want. I have been working on this for years now. "Worrying is just using your imagination to bring about what you don't want," or something to that effect.
If we can learn to monitor our thoughts, and recognize if they are negative at the very least, then we can put them in check and re-frame them in the positive, to bring about what we do want.