Knee extension exercise will help strengthen your knees, which will improve your balance and reduce your risk of falling. Strengthening your knees will also allow you to walk and climb stairs with greater ease and comfort.
Sit on a chair with your back straight and knees bent
Slowly extend your right leg out in front of you and hold for a few moments before lowering it back to starting position
Repeat with your left leg
Do 10 repetitions on each leg
For a more advanced version, strap an ankle weight around each ankle. Aim for a weight that is heavy enough to where you cannot do more than 15 repetitions per leg. As you get stronger, you can add more weight to keep it challenging.