Clark Kent actually does a lot to hide the fact that he's superman.
He changes his posture to make himself look shorter, the glasses he wears are very thick and they distort the image of his eyes quite a bit.
He also wears multiple layers of clothing to hide his physique and if anyone ever finds out how ripped he is and they start investigating him, he has a set of weights in his apartment and upon looking into his past, "oh, he grew up on a farm!"