Your small pet, like a hamster or guinea pig, spends most of his day in a cage, so he needs a good outlet for exercise.
You can purchase a tunnel system for many small pets, which extends the area in their cage and gives them a great opportunity to climb and run. If your cage doesn’t accommodate this type of exercise run, build one within safe confines where your pet can’t get loose, and let him work his way through it.
You might have to start by hiding a small treat in the tubing to help motivate your pet to move through the course.
A wheel is also a great form of exercise. Hamsters, gerbils and mice especially love to run on a wheel mounted in their cage.
Create an enclosure (outside of the cage and in a much larger space) where your pet can roam free. They will like the feeling of vast freedom that they will experience.
Small balls are wonderful playthings, as your pet will chase them.
Finally, invest in a collar and leash for your small pet. You can walk them, too.