I made a list in a previous post entitled, "Has ancient medical techniques ever proven successful?" (by u/BedsideRounds, and I realize I'm tagging myself, but that's just so the auto-mod doesn't get me). It is certainly non-exhaustive, and biased towards my field (medicine; lancing boils and extracting teeth were certainly things barber-surgeons did "right," but it's not something I'm usually super excited by) and IIRC I wrote it partially while I was on call (must have been a slow night).

Let me know if that helps, or if you have any more questions.

EDIT #1: "medieval medicine" is also a somewhat problematic term; the history of Western medicine doesn't split very neatly into discrete eras (which is why early modern medicine is so fun!), and many of the things that we associate with the medieval period are in fact quite modern. So the purpose of my list, I basically included "pre-modern" medicine.