Generally, the CDC recommends that all face coverings should:
1. fit snuggly but comfortably against the sides of the face
2. be secured with ties or ear loops
3. include multiple layers of fabric
4. allow for breathing without restriction
5. be able to be laundered and machine dried without damage or change to shape (shrink fabric before making the mask)
For eye-glass wearers, the Daily Press of Hampton, VA, has addressed the problem of glasses fogging when wearing a face mask, advising that immediately before wearing a face mask, one should wash the spectacles with soapy water and shake off the excess. Let them air dry or gently dry with soft tissue before wearing. Soap film should prevent the fogging. Woodworkers have found shaving cream works to prevent such a fogging problem. (Daily Press, April 25, 2020 by Joshua Axelrod of the Pittsburgh Post-Gazette).
In addition, see this Atlantic Monthly article on “The Real Reason for Wearing Masks”: