When you get new goggles DO NOT touch the lenses with your fingers. This destroys any anti fog properties and puts grease marks on the lens. Instead, gross as it sounds, spit in your goggles and swirl that around before rinsing the goggles in the water you are about to swim in. Repeat this every time you swim.
I’ve come across all sorts of tips including toothpaste smearing in the past but that has made my eyes sting and the above spit and swirl has delivered fog free goggles for a 6 hour swim. That’s a pretty good test!