1-have good grammar skills (I personally don't like fanfics that don't have good grammar. Even if they don't speak English. Or bad at it. I don't mean to offend those type of people.)

2-try to make the chapters longer (I like to read long chapters. You can make medium chapters. But I like to read medium or long chapters.)

3-Be Creative(be unqiue with your story, for example: 'The boy saved the danzel in distress" it's very common really. try to be creative with that)

4-Be specific(don't just in your book be like: "Naruto wore clothing." You have to be more specific like... "Naruto wore a jacket that had the Uzumaki clan crest on the back. It was black and orange. And he wore a leaf Shinobi headband" but don't be to specific like. "Naruto wore a beautiful tuxedo and it glimmered in the sun with enormous sparkles and was shiny deluxe and it was from the vip and from the hokage and wore flowers at the top and wore a beautiful yellowish tie as the tuxedo looked shinier out in the sun."

5-have punctuation marks. (the classic saying, it wouldn't make sense if it doesn't have punctuation marks. "Lucy joined the fairytail guild she was going to go get celestial keys and met natsu on her way she said "hi" and natsu said "hi" and they both went their ways and departed agreed to meet up to get a request on the board to do their mission" see it be a whole mess.

That's all the tips to writing.
Anyways bye fluffy BOIS