As a general rule of thumb when it comes to eating, try to eat foods that don't have a lot of ingredients in them.
Better yet, eat as many one-ingredient foods as possible.
Blueberries have only one ingredient: blueberries. Carrots have only one ingredient: carrots.
Kraft macaroni and cheese has 3 million ingredients in it. Even your typical 150-calorie "healthy" protein bar, that has 20 grams of protein and zero grams of sugar, is made from at least a dozen different ingredients (and some of them are probably things that you have no idea what they even are).
The more "pure" a food is, let's just say here, the less processed it is, the more nutrients the food will offer your body. Your body will have an easier time metabolizing a purer food as well.
Make sure most of the food you buy at the grocery store doesn't have any packaging at all (fresh fruits, vegetables, and lean cuts of protein).
And for the food you buy that does have packaging, take a look at the label. Look at the label not to see how many calories are in a serving, but to see what ingredients comprise this food item.