Well, for the things that I could control I'd have to say our exercise and maybe good food?
When I adopted him they thought he was already about 2 and he seemed pretty restless. So within the first month I had his walks up to ~3mi x 2 times a day and a pee break before bed. So about six miles a day if we only stuck to the 2 main walks a day. On the weekends it was almost always 3 or 4, but the distance was about the same. He (and my other Rott) kept fit, lean, had tons of mental stimulation, structure, and thirdly: plenty of exercise. A tired dog is a good dog. If he/they ever had any kind of issue I would back the walk off for a potty break and whatever they could manage, but those times were very few. But every day of his life I'd get up, plug my phone in, and we were out the door. Rain? RuffWear makes great raincoats. Snow & Cold? RuffWear. I'm not feeling it? Tough shit. He depended on me and I kept my end of the bargin. No one will ever be able to convince me that this did not impact how long he lived or how incredibly healthy he was.
For the first 1/2 of his life he was eating Merrick, which was more expensive than most of the other dog foods available but I *constantly* got comments about how good he looked, coat was shiny, eyes were bright...just a really good looking dog. And I believe part of that was his diet. Merrick changed something at some point a few years ago and both my Rotts didn't care for it so we switched to Blue Buffalo (adult, chicken or salmon?) and that has been pretty solid.
Thanks for your comment and feel free to keep this going if you have more questions. :)