What stylistic strategies does Coelho use to make The Alchemist come across as a mythic, universally applicable story?

The Alchemist, written by Paulo Coelho, comes across as mythic and universally applicable. This is a timeless story because it teaches the lesson of realizing "personal legends," or following one's dreams, and pursuing these dreams by making decisions. This is something humans will always aspire to do and will wish to learn about.
This story is universally applicable and timeless because Coelho does not use specifics in his descriptions of places or people. Although there are specific people and places mentioned, such as Santiago (the main character) and the fact that the story begins in Spain, most of the places and characters are left vague.
When Santiago describes the people he is meeting, he often refers to them as the things they represent in his life or the jobs they do for a living, such as "the merchant," "the fortune teller," "the Englishman," and "the Alchemist." Even the girl Santiago falls in love with, Fatima, is not explicitly described. By not describing these characters and keeping their identities vague, Coelho makes them more relatable to readers so that they could stand in for any person.
When Santiago describes places, he calls them by basic names like "the Pyramids," "the oasis," and "the crystal merchant's shop." These names could indicate any place, which makes them more universal to readers.
Coelho does not ever mention the time frame of this story, either. Because readers do not know the exact year or time of year the story takes place, it is easier for readers to picture themselves in the story.
All of these reasons make this story universally applicable. At least in part because of the story's ambiguity, it became an international bestseller and was published in many languages and countries.

The mythic takes place outside of history. The main stylistic strategy Coehlo uses to give his work a mythic feel is to place it apart from the historical and the specific.
The tale does start off in a place, for we are told early on that:

The girl was typical of the region of Andalusia, with flowing black hair, and eyes that vaguely recalled the Moorish conquerors.

So we know that Santiago, the main character, starts off in Spain. We learn that the story is set after the time of the "Moorish conquerors," but we are given no specific dates to know when this might be and only a general sense of place. We learn Santiago is heading to the pyramids, but we do not know much beyond that. We also know the story is set in the past, because the characters do not have automobiles, phones, planes, and other modern technologies, but it is an unspecified past—hence a mythic past. 
Also, many of the characters do not have names, but are, in fact, representative types, such as a merchant or an old woman. Again, this lack of specificity as to proper names lends a mythic, universal quality to the novel. Santiago himself is often referred to as the "boy," making him seem a mythic representative of all boys who aspire to follow their dreams.