The rules are simple. If your dog has short hair, you should probably bathe it every six weeks. If your dog has long hair, or real thick hair, bathe him or her every three to four months. Dogs clean themselves, so do not worry, they are doing the job, when you are not. The main thing to shop for is a dog shampoo.
Many people think their shampoo works fine.
But, dogs have a different pH to their skin than we do. Human shampoos will harm them. Some dogs have sensitive skin and will need a mild shampoo. You can find these at your veterinarian's office or at many pet shops. You will need to ask for a soap-free formula.