Here's some resources on understanding structure and your knees. Alignment is the most important principle to follow. The knee points at the centerline of the big toe of the foot. For the beginner, in a front stance, the front shin does not move past vertical. This limit must be respected when pushing or pulling.
Power will not pass safely through a knee that is out of alignment. The source of most knee pain is in the relationship betweent the hip and ankle, not the knee itself. A habitual misalignment, coupled with overtraining, will result in permanent damage to the joint.
Develop your awareness so that such misalignment does not occur. The Urban Retreat Center does not allow students to train improperly and damage themselves.
More about sports related knee injury from this article on Common Dance Injuries.