Prenatal vet visits are a must. Nature rarely "takes it's course" properly with dogs, and simple canine pregnancies are not nearly as common as people think.
First though, all dogs should be spayed or neutered unless they are breeding stock. Breeding stock are dogs who are proving themselves in the show ring, performance ring or work environment. "Letting Lassie have a litter, so the kids can learn about life" is a really dumb decision. Remember - for every puppy placed in a home, a dog will die in the shelter as that home is removed from the market. It's a sad fact, but true. If you allow your dog to have puppies, you ARE killing that many dogs in a shelter.
So, first and foremost, a person should NOT allow their dog to have puppies. A good breeder, even a new one, will already know the answer to the aboe question.
Also know that to breed properly takes an immense knowledge of genetics. I bet few people know that breeding a certain color of dog to another certian color of dog can cause the litter to be blind and deaf. It is true. Lack of such simple and common knowledge abounds, and only breeders who are willing to learn canine genetics should be breeding. Breeding stock also should have all health testing done (hips, eyes, DNA, breed related diseases, etc.). Breeding properly is expensive, hard work.
After a pregnancy occurs, a vet must become involved immediately. Proper supplements, exercise and food must be given to the dam. The vet needs to be involved throughout the whole process. A person experienced in whelping litters should be present at the birth. Then the puppies need to be properly raised with vet visits, proper mental stimulation and the home being prepared to keep the puppies for a MINIMUM of eight weeks. Understanding of puppy mental development and proper age appropriate stimulation and puppy personality testing should be understood and preformed.
Raising a litter of puppies, when done right, is highly time consuming and difficult. Just letting "nature take it's course" is a good way to get unhealthy puppies and puppies emotionally unable to deal with the stresses of modern day life with humans.