He can start with the basics. A simple exercise 'Sit to Stand' -
Start by sitting in a chair with your feet flat on the floor. After sitting for a few seconds, use your legs to stand up. Finish by sitting back in the chair. Doing this 10 times can really increase strength in your lower extremities, which helps to improve balance.
Just taking a walk around the block can also help.
Make sure he gets a healthy diet and avoid food items that are high in sugar.