That's an interesting topic! I believe that weight is important - thin dogs are said to live longer. Good nutrition must be important. And perhaps leading a fun and happy life so life is worth living.
A good reply from Janet, I agree with those points. Being descended from a long living bloodline is a great asset too, and often something we don't ask about when choosing a dog.
A species appropriate diet and adequate mental stimulation and physical exercise. Oh, and bags of love and a happy life
I truly believe what helped my parents' large lab mix live until 13 years old was the fact that they got a puppy when the older dog was around 9 or 10 years old. The puppy got the older dog to move around and play a lot more than he would have had he been the only dog. All other responses to this thread are great as well!