If you wear glasses like me, you are probably quite frustrated by the fog which the mask creates on your glasses, especially in winter. This simple origami design, folded from paper handkerchiefs, tightens up your mask and thus reduces fogging. While this solution is not perfect, it works quite well and is easy enough to fold that using it in real life is reasonably practical.
The main disadvantages are that the seal created by the fog stoppers may open up when you move, especially if you talk while wearing your mask, and the loose corners which stick out in front of your mask and may limit your field of view if the wind blows them up. The latter can be prevented by holding the corners in place with the help of band-aid. It is quite important that this solution uses two separate fog stoppers rather than a single one: this way the nose is free from the tissue paper which allows the mask to be laid out is a straighter line, reducing air leakage.
As for alternatives, my favorite is to use a single long strip of adhesive bandage (sold in rolls at any pharmacy) to affix the upper edge of the mask to your face. While detaching the mask can be a bit unpleasant, this method is quite fast, and the most effective one I know of in preventing fogging of the glasses (yes, I do think it is better than the origami solution). An important culprit to watch out for is that you have to attach the whole upper edge: if you only use the band-aid on the central part, you will still get fogging form the air flowing around it. Another solution is to use the better N95/FFP2/KN95 masks instead of plain surgical masks: in my experience, these stiffer and less permeable masks also reduce glass fogging significantly.