One of the most important things is to stay fit. Plan on hitting gym six days a week. It's important when you're young but mandatory when you're over 50. Best book on the subject is Younger Next Year by Chris Crowley and Harry Lodge. Very informative and very motivating.
They also wrote a follow on book called Younger Next Year for Women which I've not read but which I assume covers the details the first book did plus hormonal issues.