While the physical appearance of all of these beasties is variable, they share a number of characteristics. Like all fairies they have the ability to become invisible at will, and all seem to possess the ability to traverse vast distances with magic. All have an intimate connection with nature.
Elves tend to be tall and slender and spend most of their time dancing in the woods.
They are fantastically beautiful and to look at one is to go stark raving mad from desire. Leprechauns also have an affinity for the wilderness, but look more like dwarves and speak with annoying Irish accents. What unites these three races is their general desire to avoid people. That don't necessarily dislike humans, they just see us as trouble and want to stay away from us. Dwarves just because we are a nuisance, Elves for the same reason that girls abhor obsessed lovers and Leprechauns because humans are always trying to steal their pots of gold.