I often see people cycling with their knees almost at right angles to the bike, which puts abnormal stress on the ligaments of the knee. This is caused by pointing your feet outward, pulling the knee with it. Similarly, pointing your feet inward will lead to ligament stress. Overloading the muscles of your leg by pushing at a high resistance for long periods will also damage the ligaments surrounding the kneecap. To prevent this pay attention to setting up your bike, making sure that your saddle is at the correct height, and that your feet are in a comfortable, neutral position when you ride.
Rest is the only cure for cyclists knee.
We all know that no-one is going to stop cycling all together, so reduce the amount of training you do until the condition settles. If your knee is hurting you continually, then halve your training schedule until the discomfort has gone. However, there are times when excessive, prolonged pressure can lead to nerve and tissue damage. For example, pressure between the hands and the handlebars can lead to damage to the ulnar and median nerves, since they can be compressed between the bones of your hands and the handlebars. You have problems with the ulnar nerve if you have pins and needles and numbness in the ring and little fingers, and problems with the median nerve if the symptoms are in your thumb, index and middle fingers.