I'm pretty short sighted and I've been wearing glasses for ages, so this is something I have experience with. Let's just state that there is a reason I use contact lenses for outdoors activities.
If you think glasses are bad, try fitting a pair of skiing googles over a pair of glasses... Then you have 4 glass surfaces that can fog, multi-layered glass in the ski googles not included. Each surface will have its own temperature, at least one of them will fog. Been there, done that.
If you have to cover your face, always make sure the air you breathe out has somewhere else to go than up along your nose to your glasses.
The real hard part is if you're doing heavy physical activity, such as high intensity aerobic training. Then you have to went away moisture and keeping a strict "ventilation discipline". I.e. if you're running, skiing or cycling, your speed provides airflow to keep those glasses clear - then don't just stop at any random spot - stop somewhere in the wind so you can ventilate your glasses. When you stop, loosen any head garment that can obstruct air flow.
Also, it's an either-or situation: Either the glasses / googles must be "cold", i.e. well ventilated so moisture from your eyes is vented away. Or they must be "warm", i.e. so warm that moisture doesn't condense on them. Most of the time, keeping them "warm" enough is close to impossible, but you could do it with a pair of glasses that you seal off under a pair of skiing googles. But when you seal them off you have a buildup of moisture that is not vented away. In other words, it works well for a while before it fogs like crazy. Not good. Keep 'em cold and well ventilated is usually the best bet.
Some anti-fog chemicals are rumored to be effective, but I have little experience with them.