what's the least painful way to propagate monstera?

Cut just below a node - the brown bump where a leaf joins the stem - and make sure the cutting has at least one node on it, ideally with an aerial root. A leaf on its own will sit in water and never become a plant, which is where most people go wrong. Jar of water somewhere bright but out of direct sun, change the water weekly, and pot it up once the roots are a few inches long.