Here is an excerpt from my book, The Silent Master: Awakening the Power Within:
Just as you purify your thinking by choosing what thoughts and words you will concentrate on, you must purify the images that you visualize. You can use the previous six part meditation that we used for concentrating on an idea to use for your visualization. Instead of dwelling on the words that describe an idea you want to manifest, dwell on the picture of your desired manifestation. During that time, allow no other pictures to enter your mind.