Visualization is the ability to see clearly something in your mind, to be able to touch, taste and hear with the inner senses of your mind.
Our eyes do not actually "see." Nerve impulses are brought on by light stimulus and are sent to the brain. It is the brain that translates these impulses to images.
Visualization is very important if you wish to be successful in working with spells and ritual. It is the most powerful tool humans have. Imagination is what moves us forward as a species.
You will need to work in the positive, as if your wish has already manifested.
You may wish to find meditation and visualization tapes to help you along.
Visualization takes practice, and more practice. You will be creating an image of what you want. You will see it. But do not force it. Everyone progresses at a different rate.
Try to do one of these exercises once a day. Do not get discouraged and keep trying.
Some find visualization easier than others. All improve with practice.