I wear safety glasses on a daily basis. One thing that I have learned is to keep a gap between the top of your glasses and your eyebrows.
If your like me and quint a bit when your shooting, my glasses will press up against my brow and fog.
I also keep a small cotton towel in my range bag and regularly wipe my eyes, eyelids, above my eyes, bridge of my nose, and eyebrows.
Basically, reduce moisture and allow airflow.