There are six steps you can take to prevent dog snoring, but not all apply to every home and situation.
1) If allergens are the issue, clean the dog's bedding on a daily basis. Only take him on outdoor walks when there's low levels of pollen and traffic. Regular vacuuming helps immensely.
2) Don't smoke around your dog. Better yet, don't smoke indoors at all.
3) Use a product like Snore-Stop.
4) Vets can sometimes do surgery when a breed that is predisposed to snoring is still at a young age.
5) Regular exercise and weight loss sometimes reduces snoring in dogs, just like in people.
6) Try repositioning your dog's physical sleeping pose. Do this through a change in bedding or possibly even a pillow to elevate the head.