Nine

Don't use abbreviations when to write a book (like LOL or WTF or TBH etc.)

Your perfect seventeen-year-old protagonist does not need to have waist-long hair. I have waist-long hair and it isn't as easy to manage as you make it sound.

We get it. Harry Styles has curls.

Think of writing a fanfic in this way: if you showed it to the original fic's writer, would s/he appreciate it?

Describe your areas properly. As in, if they are in a house, give the readers a general layout of the place.