Invisibility

Invisibility is how to master the art of Not Being Seen.

Ancient mythology is full of stories of how protagonists find magic items which ensure they cannot be found; the most famous being the ring of Gyges by which he was able to usurp the throne of Lydia. It was long asked among the Greeks if Gyges could have done anything other than crime since he now had the power to get away with it. Tolkien had an answer to that.

This is one of the old mainstays of Dungeons & Dragons spells, and potions, and of course rings. It takes several forms: full transparency, redirection of light, camouflage, or simply hiding in shadows.

From an optical perspective, transparency is the worst option since the lenses in your very eyes will fail to refract light to your cornea - you'll be blind! Although, Tollers saw through this one and did, in fact, allow that the invisibility is not total, so you will cast a slight shadow.