Eat real food, not too much, mostly plants.
Vegetables, fruits, whole grains, and, yes, fish and meat. Be able to pronounce the ingredients and keep the ingredients to 5 or less.
NOT TOO MUCH
Eat to support your goals and activity level, not body fat. Tracking overall caloric and macro nutrient intake can be informative to see if you’re eating too much or even not enough.
Don’t eat something that won’t rot. Yes – honey is an exception here but foods that last weeks and weeks are typically packed with preservatives you don’t need.