Wearing a ring of levitation causes you to levitate. It is a highly desirable item since some levels, such as Medusa's Island, the Plane of Air, and the Plane of Water, all but require levitation. The ring is safer than temporary methods of levitation, such as potions or spells, and is more convenient than levitation boots as it does not take up an armor slot.
Levitating over a sink removes any sources of levitation and causes you to crash to the ground; this can be useful in removing a cursed ring of levitation, or a ring of levitation under cursed gloves.
Identifying a ring of levitation could not be any easier; just put the (ideally noncursed) ring on and see if you begin levitating!
Dropping a ring of levitation into a sink produces the message, "The sink quivers upward for a moment."
In the beginning stages of the game, a noncursed ring of levitation is especially useful for roles that have ranged attacks or very weak physical attacks. As there are very few monsters in the early game who ignore Elbereth, simply Engrave Elbereth in the dirt and put on the ring. Monsters will then turn to flee, and if you are patient enough, you can dispatch them at your will, as levitating, and even fighting, above the dirt will not erode the engraving.