Eat food. Mostly plants. Not too much.

(selectively excerpted from Michael Pollan's In Defense of Food)

Don't eat anything your great-grandmother wouldn't recognize as food.
Avoid foods containing unfamiliar or unpronounceable ingredients.
Avoid high-fructose corn syrup.
Avoid food products that make health claims.
Shop around the periphery of the supermarket.
Shop outside the supermarket whenever possible.
Eat mostly plants, especially leaves.
You are what you eat eats too.
Eat like an omnivore.
Eat well-grown foods from healthy soils.
Eat wild foods when you can.
Eat out of a traditional food culture.
Regard nontraditional foods with skepticism.
Don't look for magic bullets.
Have a glass of wine with dinner.
Pay more, eat less.
Eat meals, not snacks.
Do all your eating at a table, in the company of others.
Eat slowly.
Stop eating when you feel full.
Cook.
Plant a garden.