"Eat slowly."
Take the time to savor your food and you'll feel more satisfied with less. There's an Indian proverb that states, "Drink your food, chew your drink." In other words, chew your food thoroughly enough that it is liquefied (great for your digestion, too!), and take the time to roll your drink around in your mouth before swallowing it, so you can truly experience the taste. Or, here's another one you've probably heard but don't often apply; "Put down your fork between bites".
All the tips given for the 28 Days of Real Food Challenge were compiled from "Food Rules", by Michael Pollan.