Have too much knowledge or too many skills, and you’d get yourself burned alive as a witch.
I think I would prefer to go back in time on this continent and bring a more primitive civilization forward. The Aztecs thought the Spanish were Gods and that’s a safer bet.
You could bring the civilization forward while quietly converting them to Christianity.
Cure a thousand people, but fail to cure one who was beyond help, especially if that person was a king or lord, and you’re still toast.
In Mark Twain’s “a Connecticut Yankee in King Arthur’s Court” a visitor from Twain’s present saves himself from beheading by commanding that the sun go dark as a demonstration of his power. Conveniently, and however far-fetched, he knew the exact time and date that a total eclipse of the sun was about to occur.