First, put all that energy you are wasting on worry to better use. The numbers are not nearly as glum as the TV news would have you think. Generally, the best prevention is to eat a diet primarily consisting of raw fruits and vegetables. Roasted or steamed is ok too, but raw is better. Berries are low in calories and high in the good stuff, so try to have them in the mix.
Vitamins can be good, but do not go over board. Do some regular exercise, including weights.
Invest some time and cash in research - subscribe to "Prevention" or other journal of healthy living.
Oh yes, see a doctor at least once a year for blood work and check up.
Good Luck!