Perhaps most important is to have lots to do. It doesn’t matter what it is, but whatever you do in retirement should take a lot of effort. For me, it was house-building and ultra-running.
Be sure to keep up on exercise, with a healthy lifestyle. Try to get at least two hours of aerobic exercise each day. Be very careful about diet. (Editor’s note: Rich ran his last marathon in April 2013, at age 81.)