Great advice! You can also find more information on how to exercise your knees in our fitness center and our latest feature article. Strong knees with strong muscles are less likely to get injured.
This article summarizes the Harmoknee Preventative Training Program which provides a list of different warmup drills that will help prevent serious injuries to the knees. It's great for all sports, including volleyball. The article goes on to list other sites for information including the American Orthopaedic Society for Sports Medicine and the Women's Sports Foundation.