1) Start with a clean pair of glasses. This goes for your scuba mask, too! Use your dish soap: It is a fabulous de-greaser! Clean both inside and outside lenses, nose-piece, ear wands... all of it. Leave to dry or dry with a soft micro-fiber cloth.
2) A close fitting nose piece on your mask will reduce the fog exiting the top of the mask onto your glasses. Re-bend your nose wire (if it has), use a buff, situate it a little lower on your nose bridge (but still wear it properly! Cover those nostrils!)
3) When I know I will spend all day in glasses/mask combo, I clean my glasses that morning!
4) Our goggle/eyewear defog spray is made for this purpose: Spray both sides and clean dry with a cloth. DO NOT USE concentrated scuba defog, meant to be used with water! Check the print on your defog: Goggle defog is already watered down for use that close to the eyeball.
5) Hey! While you are at it, get your scuba mask out and give it a clean! Use that same dish soap! Then allow to dry and store in it's box. If you have a neoprene mask strap, remove it from the mask while in storage: Neoprene off-gasses and discolors silicone mask skirts. We will be back using that spotless and non-discolored scuba mask in no time at all! Promise!