The previous post was quite strong. I would also say that one of the ways Tolkien has conveyed fantasy was through the philosophical battle of good vs. evil. Sauron being the embodiment of pure evil has implications of a fantasy notion. What does evil look like? If it were to be personified, how would it act or carry itself? The eye that is always attune to the ring and its bearer helps to convey this "other world" element to it and, in the process, captures an element of fantasy. It is real interesting to see that philosophical inquiry, a strong theme in Tolkien's work, takes on this fantasy quality. The fact that human beings are pitted in this battle between good and evil only heightens the idea that the quest for the ring and the need to destroy it has both philosophic and fantasy based implications.
There is an excellent discussion of how Tolkien uses fantasy right here on enotes at the link below (click on the right column under "style"). Essentially, fantasy is a genre that deals with the unreal, the supernatural. An alternate world is created, in this case "middle earth" and the alternate world has different values than the real world, usually better values. Magic is an element of fantasy, so it often contains non-human creatures (elves, Hobbits) and the creatures usually possess powers and qualites that humans do not. Sometimes one enters the alternate world from a portal. Often, a fantasy is an allegory.
Check it out at the link below.
The cliche battle between good and evil is one of them. This is the most important factor in any fantasy novel or movie. Sauron is utter evil and the battle of the ring and to bring the dwarves justice takes on a whole new role. Similarly, within Lord of the Rings and the Hobbit, the hero follows the 11 Stages of the Hero by Campbell.