Here are some of Knee Stretches Exercises which will probably help you in maintaining the good condition of your knees:
Extending your knee while seated on a chair. You are relaxing your foot on the chair while your knee is slightly raised. The raised knee will now be push a little bit forward towards the floor using your legs. You are going to hold it for at least 5 to 10 seconds then release. Do it for at least 5 times for each knee.
Lying while extending your knee. You are going to lie down on the floor together with the bended left knee and flatted foot on the floor. Sliding your left heel far from your body you will now have parallel legs. Hold it for at least 5 to 10 seconds until you are finished it doing 5 times using both legs alternately.
Stretching your knees using a towel. You are going to sit on a chair and put a towel under your left foot. Put a force on the towel by slightly pulling it using both of your hands to make the knee bent raising your foot for at least 4-5 inches high from the floor. Again hold it for at least 5 to 10 seconds and do it 5 times for each leg.
Confine stretching of your knees. You are going to stand and place one foot in front. Using your hands put a little force in your back and make the opposite knee bent together with your hips until you felt the that it your arm and knee are already been stretched. Hold it for 5 to 10 seconds and repeat it 5 times.
Quadriceps stretching exercises. You are going to hold on something for your balance like walls and chairs. Then lift one of your feet and raised your heel near your buttocks. Take hold of your ankle and pull your heel a little bit closer in your body. Hold it for 5 to 10 seconds and repeat it for 5 times.