I think it differs for everyone, but I can only get a good seal by having the top of the mask (with the bendy metal bit) well down my nose, so the metal bends down into the "crease" bit on the outside of my nostrils. If I have it higher near the bridge, inevitably air comes up my cheeks and out to fog my glasses. My nose is fairly big, I suppose.

Oh, I've been wearing my mask wrong... My glasses fog up as well, and I've been putting my mask at almost the same height as the lower frame of my glasses...

Realistically, with cheap masks you really can’t. I tried all the “life hacks” suggested and none of them work, some fogging inevitably happens.

The only way is to get a proper N95 or N99 mask, which has padded edges that make for a proper seal. You’ll also be safer.

Literally impossible if you have a big nose.