Aw thank you so much! I guess just make sure you're writing something you're passionate about, whether it's about Marvel or any other fandom, or even a story of your own. I think that's the most important thing.
Other than that, pay attention to your punctuation, paragraphing, and grammar (I sound like my English teacher wow). Also, make the book kind of relatable? I don't know if that makes sense, but I think that the sense of familiarity from the character is important to the reader.
I think that's all I can say haha. Hope this helps!