Chewing is a natural pastime for dogs. Puppies will chew especially when teething.
Chewing can also be a sign of boredom. There are toys that are available which can be filled with treats. This encourages your dog to work for the treats.
Make sure your dog has plenty of exercise and is not left alone for long periods.
Chewing can also be a sign of stress and anxiety. Consider using a Dog Appeasing Pheromone. This is a natural solution which can be sprayed onto your dogs bedding and living area. It appears to have a calming effect on dogs.
Consider joining an agility class, fly ball or obedience to entertain your pet.
Some dogs chew to draw attention to themselves. The owner offers the dog a treat or chew and the dogs see this as a reward for his destructive behavior.
Make sure chewable objects are out of reach from your pet is he is left unattended.