I find that to make a TRULY popular fanfic, you don't necessarily have to be good (although that can certainly help) but you do have to be FUCKING BIZARRE. You write a wonderful, in-character, so-close-to-the-style-of-the-work fanfic and everyone in the fandom will love you. You write about Link and a girl drinking each other's urine as they get married ... well, you'll get a lot more readers, at least.