1. Stay slim, staying slim reduces the forces placed on the knee during both athletics and everyday walking and may, according to some medical research, reduce osteoarthritis. Keeping your weight down may also reduce the number of ligament and tendon injuries for similar reasons.
2. Keep fit. Many knee problems are due to tight or imbalanced musculature. Stretching and strengthening, therefore, also help to prevent knee pain. Stretching keeps your knee from being too tight and aids in preventing both patellofemoral syndrome and iliotibial band syndrome. Strengthening exercises particularly of the quadriceps (straight leg raises and leg extensions are two excellent exercises, but please see a book on exercise and training for more) can help prevent knee injury.
3. Exercise wisely. If you have chronic knee pain, consider swimming or water exercises. In water, the force of buoyancy supports some of our weight so our knees do not have to. If you don't have access to a pool or do not enjoy water activities, at least try to limit hard pounding and twisting activities such as basketball, badminton, or jogging. You may find that your aching knees will act up if you play basketball or Badminton every day or twice a week.
4. Protect the knee. Wearing proper protection for the activity at hand can help avoid knee injuries. When playing volleyball or when laying carpet, protecting your knees may include knee pads. When driving, knee protection may include wearing a seat belt to avoid the knee-versus-dashboard injuries as well as injuries to other parts of your body.