first of all, my mother is an optician, that means the works in sales at a store that sells glasses. So that store anyways offers very good service and you can guess that my glasses are fitted quite well and therefor dont slip often.
If they slip I usually push them up with one hand, but with my thumb on one corner and the other fingers on the other corner, its a habit from when my left hand was broken.
SO I belong to that camp of people doing it that way, like Shax and Zantos, but when Im in a conversation I usually just grab the rim of the right lens to fix them, so I dont block my vision of the person Im talking to.