There's the obvious eat right, don't smoke, moderate everything, exercise, annual checkups, of course. You could also run a genetic test to see what you're most susceptible to and adjust your lifestyle accordingly.
But there are a ton of other things that you could obtain regardless. Even with Tbi, it's common to suffer what appears to be a minor injury at first, don't even see a doc for it, and then 5 years later you're suddenly having problems and no doctor can figure out why. Or maybe you had a bad virus one year and it you assume you got over it, forget about it, then years later your body is messing up. There are so many chronic illnesses where you'll find a mix of people from all types of lifestyles from the huge party animal to the avid runner and yoga enthusiast.
It's hard to say that going to a doctor often could somehow prevent these types. They can barely figure out what's happening while you're going through severe symptoms so there wouldn't be much they could see before it got to that point.