Answer:
The same similarities as can be found also with the Matter of Britain (Arthurian legend) and the New testament:
The hero is marked, either by a sign on his body, an object, or a circumstance (lightning scar, One Ring, controversial birth).
The hero has been prophesised
The hero must die (several twists to this).
The role of the traitor (Judas, Gollum, Snape, Mordred) is ambivalent and extremely complex.
All the traitors are sacrificed.
It is basically a fight between good and evil as personified by a marked hero fighting a super-villain (Satan, Morgan LeFay, Sauron/Melkor, Voldemort).
There is a price to pay for redemption
The hero generally does not get to enjoy the peace he sacrificed himself for, Harry being the one exception: “It must often be so, Sam, when things are in danger: some one has to give them up, lose them, so that others may keep them.” Says Frodo to Sam, on his way to the Grey Havens (LOTR III, The Return of the King).
Apart from this, there will be details and accessories that are common: Shelob/Aragog, Sword of Gryffindor/Excalibur, resurrection after death (Harry/Jesus), the notion of never-dying immortality (Jesus, Arthur the Forever King, Frodo)
