The Arthurian tales dating to the 12th and 13th century generally describe the practices of the 12th and 13th century.
Bleeding was common. Supposedly only bad blood came out. It was considered a social occasion. Leeches were often used.
Various medicines and salves were used. They are not normally described.
At least some authors had a low opinion of medical knowledge. According to the “Tristrant” of Eilhart von Oberge, when Tristrant was badly wounded, various physicians attempted to heal them. One young physician who had recently been taught at Salerno tried to indicate that the other physicians didn’t know what they were doing. But the others only mocked him, and eventually the young physician went away. Eilhart claims this young physician would have killed Tristrant if he had been given the chance.
Tristrant in other romances is the same person known as Tristan and Tristram.
There is a tendency to sometimes turn over healing to women. Iseult, Tristan’s lady-love, is especially well known for her knowledge of healing and healing herbs. She originally healed Tristan when he arrived crippled in Ireland from the poisoned wound given him by Iseult’s uncle, the Morholt.
See http://www.intermaggie.com/med/healing.php and http://en.wikipedia.org/wiki/Medieval_medicine .
Occasionally magic is used or mysterious herbs. In the “Perceval” of Chrétien de Troyes the author tells the folk take of a weasel whose mate is cured by is restored by a mysterious herb. Gawain knows this, and obtains the herb to restore an injured knight. Chrétien’s story of “Erec and Endie” refers to a drug which Arthur has from his sister Morgain which is used to heal Erec. In Chrétien’ Yvain a lay of a castle has Yvain healed of his madness though a drug rubbed on his temples.
Lancelot is restored from madness by being forcibly placed in the hall where the grail appears at night.
Usually a knight who is badly wounded ends up being treated by a hermit and the healing seems to consist mostly of quiet and rest.