I want to edit my one shot and make it better grammatically, but Idk how

So, I finally finished my first one shot (YAY!). Had tried writing a lot of WIPS in the past and finally made one until the end.

But now I'm trying to edit it to make it better. And I feel like I'm looking into a wall without knowing what to do.

For context: I'm not a native enlightened speaker. I'm writing in English because it's the language that my fandom is most popular in. Therefore, I'm not that good at grammar. I have done an English course in the past and, because I've been reading practically everything online in this language, I have absorbed some rules. But I feel like when I read my one shot the English is not quite right. It is clunky. The things that happen are interesting to me, but they are not having the same impact because I don't know how to use the language well yet.

I have beta readers, but I want to try teaching myself how to make the text better on my own so I can improve and don't make my friends do the same work all the time when I show them a new piece.

I've bought a book that I saw others saying is a good book about grammar: The elements of Style and I'm also trying to read Reading Like a Writer to learn how to read and learn actively. Also, I'm trying to read more books in English.

Nevertheless, I'm still having problems with editing my draft to something that feels more coherent and fluid. Anyone that has already gone along this path has any tips for me?