The best way to keep a dog healthy is to provide them with a balanced diet, adequate exercise, regular veterinary check-ups, and plenty of love and attention. Additionally, it is important to keep their living space clean and free from hazards. Grooming should also be done regularly to keep their coat and nails in good condition. Lastly, providing your dog with mental stimulation through activities such as obedience training, puzzle toys, and playtime can help keep them mentally and physically healthy.