There is a scene in Fellowship where Galadriel takes Sam and Frodo to her Mirror. It is here that we glimpse into the power rituals of the Rings of Power.
Galadriel tells Frodo, "Do not be afraid! But do not think that only by singing amid the trees, nor even by the slender arrows of elven-bows, is this land of Lothlórien maintained and defended against its Enemy."
I think that this strongly hints that it is Nenya, Chief of the Three Elven Rings, that is the "backbone", if you will, of the "magick" of Lothlórien and her defences against Sauron. If not Nenya, then certainly it is a reference to Galadriel Herself.
Galadriel goes on to show us how her Ring enables her to know the mind of Sauron:
"I say to you Frodo, that even as I speak to you, I perceive the Dark Lord and know his mind, or all of his mind that concerns the Elves. And he gropes ever to see me and my thought. But still the door is closed!"
Several VERY important clues in the above statement! Galadriel can see into the mind of Sauron, at least what he's thinking about the Elves, (which is probably quite a lot, since He's always been obsessed with besting them!). HOW can she do this?
It's GOT to be Nenya and Nenya's connection to the Nine Rings of Man that Sauron now wears. Plain and simple. Those communication lines are connected. Therefore, Gandalf and Elrond must also be able to see into the mind of Sauron, at least to some degree.
"And he gropes ever to see me and my thought. But still the door is closed!"
How is Galadriel, then, able to shut out Sauron seeing HER thoughts? Simple: Nenya is mightier than the Nine. That must absolutely infuriate Sauron, too, don't you think? We also get a short yet telling glimpse into the magickal use of Nenya:
"She lifted up her white arms, and spread out her hands towards the East in a gesture of rejection and denial. Eärendil, the Evening Star, most beloved of the Elves, shone clear above. So bright was it that the figure of the Elven-lady cast a dim shadow on the ground. Its rays glanced upon a ring about her finger; it glittered like polished gold overlaid with silver light, and a white stone in it twinkled as if the Even-star had come down to rest upon her hand."
At this point, Frodo guesses that Galadriel is wearing a Ring of Power, and Galadriel confirms it. She declares that she is the Keeper of Nenya, Chief of the Three.
So, what specific magickal clues do we get from this passage? It is clearly evening at the time when the Evening Star is high in the sky and shining down with a bright light. The light of Eärendil, the Silmaril shining upon his brow, ignites with the power of Nenya and Galadriel grows in power; shortly thereafter, she contemplates the use of the One Ring and becomes:
"Tall beyond measurement, and beautiful beyond enduring, terrible and worshipful."
In short, in the presence of Frodo and Sam, (Sam being oblivious to the whole ritual), Galadriel draws down the power of the Silmaril, of the Starlight, of the light of the Two Trees.
This gives us even more clues as to how Elven magick works and how to work it ourselves, (with THEIR blessings, of course!)