Learn to eyeball food for appropriate portion sizes.
Here are some examples from the U.S. Department of Agriculture:
Cheese – 1 ounce looks like 4 dice

Meat, poultry, or seafood – 3 ounces boneless cooked weight, from 4 ounces raw =
deck of cards

Dried beans – ½ cup cooked or ½ baseball or rounded handful for an adult

Raw leafy vegetables – 1 cup or 1 baseball or fist of an average adult
