Visual learners in general prefer seeing - videos, textbooks, diagrams, etc. Visual/non-verbal learners love the information to be organized into diagrams, charts, pictures, and tables that use form and shape rather than words. Observation has even led the people at Grapplearts to realize that visual learners ask to "see that again", rather than to hear information repeated. Our language reveals how we learn best, even without our knowledge.
In the beginning of the session, ask them to write down what they would like to discuss and questions they may have about the material. This will help them get their ideas out of mind and solidly on paper.
Create visual representation whenever possible - draw the structure of an essay using boxes, for example, or use charts showing characters and information from a novel. You can also encourage the use of computer programs like Microsoft Excel for this purpose.
Brainstorm together! Use mind maps and have them draw whatever they're thinking about, without limiting their creativity.
Refer the student to videotapes (and not just the boring ones!). If they need to write a paper about the Civil War, recommend the film Glory. Accurate, interesting movies can spark more interest than a droning documentary.
Many visual/non-verbal learners are extraordinarily creative. Encourage them to set aside some time each day to pursue a creative outlet, such as sculpture or drawing. They'll be less stressed when it comes to studying.