It depends on which practices you're looking at. Sure, they didn't have germ theory, but they did have good senses. I commend to your attention the following previous posts:

• u/BedsideRounds has a non-exhaustive list of Stuff That Worked;
• u/BRIStoneman presents Bald's Leechbook, a medical text from 9th Century England;
• u/sunagainstgold talks about medical education in the Late Middle Ages.

Bonus: u/BRIStoneman does link to it in their earlier answer, but for the convenience of anyone wanting to read the original, Bald's Leechbook is available in all its digitised glory here.

And of course, anyone wanting to continue the fight against Common Knowledge of Medieval medicine is more than welcome to have a go! More insight is always welcome.