Public baths. Not on the same scale as they were in Rome, but it was still pretty common to have a bathhouse in medieval Germany and surrounding places to bathe in a group in a large tub of hot, fragrant water, called a “Zuberbad” in German. Now everyone’s all hung up nudity. even among friends, so it’s way less common (although you can still enjoy a public Zuber bath at medieval markets and renaissance fairs in Germanic countries).
Not taking a bath
Leeches, bloodletting and general medical hocus pocus.
Carrying a sword.
Thinking God could save you from the plague.