Get as much of your nutrition as possible from a variety of completely unprocessed foods.
Boiled down to the essence, that would probably be the simplest food advice you could ever get.
That doesn't mean you should skip out on reading all seven, incredibly simple rules for better eating.
If you want to eat something processed (like tomato sauce), make it yourself. I put these in a pan and let it simmer for an hour, not stirring once. Cooking can be easy.