what exactly are you looking at specifically?
currently most ranks are based on views. if you have more views you are higher in the list even if you receive worse ratings or less favourites than those below you.
additionally, tags and genres themselves have ranks so if you include a tag that few other stories use and you see good view growth, you will rank much better than on the list of another tag that has more stories using it. you can have just 100 views, but if there are only 7 stories for a particular tag and you have more views than some of them you will find yourself ranking "highly"