In this day and age this is the question. We can do one of two things or a combination of the two. Position the glasses and mask differently and or use anti-fog spray. The fogging comes from the exhaling of hot air and if the mask isn't positioned properly it'll be funneled right into the space between your glasses and your eyes. In that area it hasn't had enough time to cool, hence the fog. If we increase the size of that space by positioning our glasses over our mask, and not before it, we'll channel the air differently and allow enough space for the hot air to dissipate. Also we can buy anti-frog sprays and apply them to our lenses for added protection. Do your research, find one that works, and use it in conjunction with proper glasses positioning to reduce fogging.