Slow and progressive increase in the amount of activity. Demonstrate modifications of exercises for different intensities or fitness levels. Give individual feed back. Tell the purpose of the activity. Teach exercise principles and use them in programming.
Older people dehydrate easily.
Exercise in a cool environment. As we age, our bodies do not cool themselves as efficiently. Wear good shoes designed specifically for exercise and replace them often. If exercising inside, try to exercise on a suspended wooden floor such as you find in gymnasiums. Concrete or carpet could lead to injury.