I've used an anti fog spray on mine, forgot the name, you can get it at ski shops, motorcycle shops or the drugstore. The best anti fog stuff I used was in a little tub, and you applied it like a wax.
It seemed to help..
Also, using the better dust masks with the foam nose gasket and metal band to form fit it to yer schnoz helps.
3M makes a nice dust mask with an exhale valve, those are the shizz.
If you warm your glasses up some before you put the mask on, put them under your arm or inside your shirt for a spell, they don't condense the moisture out of the warm exhalation breath so bad.
That's what I do, or I just don't wear glasses. ( I shut my eyes when I grind...do my best work in the dark...