Source: Creative Visualization by Shakti Gawain. To use creative visualization it is not necessary to believe in any metaphysical or spiritual ideas, though you must be willing to entertain certain concepts as being possible.
Imagination is the ability to create an idea, a mental picture, or a feeling sense of something. In creative visualization you use your imagination to create a clear image, idea, or feeling of something you wish to manifest. Then you continue to focus on the idea, feeling, or picture regularly; giving it positive energy until you achieve what you have been imagining.
For creative visualization to work effectively, you must have a true desire to create or have that which you have chosen to visualize. The more you believe in your chosen goal and the possibility of attaining it, the more certain you will be to do so. You must also be willing to accept and have that which you are seeking rather than the comfort of just pursuing the goal.