Superman actually does a lot more than just glasses to hide that he's superman. In addition to that and doing his hair differently...
He wears multiple layers of clothes to hide his physique
He has a set of well-used weights in his apartment in case anyone figures out how ripped he is.
And anyone who looks into his past will find out that he grew up on a farm bailing hay and handling livestock.
"Oh, no wonder he's so huge and ripped! He works out and grew up on a farm!"