First, understanding the themes in Naruto is vital. Naruto is about friendship, hard work, and following one's dreams. Your fanfiction should uphold these values. Second, the power levels of the characters. You can't suddenly make a minor character extremely powerful without a proper explanation. It has to be in line with the Naruto power - scaling. Third, the cultural aspects. Naruto has a unique Japanese - inspired cultural background. Incorporating this into your fanfiction makes it more authentic.