One of my friends got somewhat interested in it because of music. I then introduced some characters, one-by-one, along with a few jokes, and he eventually got somewhat interested in it...
...That is until he got himself into Homestuck.
my hopes and dreams are crushed :qq:
Basically, if the person likes video games, you can introduce the games/soundtrack to them. If the person likes anime in general, you could probably introduce the characters first, and then onto the other aspects. If the person likes fantasy-roleplaying-board-game-type-things-i-dont-even-know-what-to-call, then you could introduce the world of Gensokyo itself and the many species and landmarks that reside in it.
It really all depends on the person.