The major point in keeping a healthy lifestyle is to keep fit and to keep moving. Being active and mobile allows you to keep your muscles tone and trim, and also maintains a circle of benefits for your health. Of course, having key balance is still needed. Having balance also benefits your knees.
Always be fit and trim. At least in a good sizable body that warrants your build. Your heart would not be the only one desperately pumping blood around your body. Your knees would also experience a whole load of stress. Just imagine this tiny part of the body carrying almost all of your upper body, hips and thighs. No wonder there is much ruckus about the knee, it almost carries the same strain as your heart!
Shoes can also decide what your knees will experience. As a guy, one would go with the obvious choice of going with shoes that fit your feet well and doesn't look half as bad. For the girls, keep with one-inch heels. Anything beyond that and you would end up straining your feet and your knees. Padding on the heels relieve stress from your knees, so make sure there is an ample quantity below it.
Common sense here but avoid anything that requires strenuous amounts of knee-destroying exercises. Impossible squats are some of them, and just imagine subjecting your knees to more stress and strain after a day's walking and standing. The only time your knees will see rest is when you are asleep or sitting. The little things that we do everyday accumulates and ends up destroying our knees.
Improper body posture, retroactively affects your knees as well. When you notice that your knees are quivering, it means that the stress of the weight of your upper isn't balanced at all in distribution. Some of it goes to your femur, while others to the lower leg. This hastens degeneration of your knees. Seeing a doctor immediately is advised as this could become critical in the later years of your life. Keep a healthy diet and avoid calcium-leeching activities like smoking and drinking soda. This could prevent your legs from becoming more deformed.