ARE YOU GONNA WRITE THE ONE YOU SEND ME LAST TIME? I forgot to turn off caps lock lmao

1.get a beta reader to help u out with grammar & such
2. READ, READ, READ (It'll help u out in a long run)
3. if writing a multi-chap, plan the whole thing out ( i tend to do drafts,rough drafts, then post up the official one)
4. if u wanna be a better writer, keep practicin
(ex: keep a journal, jolt down random ideas, dreams, feelings..whatever it is, so tht later, it'll help u come up w/ a plot for a specific fic u migh come up with)

im not a native english speaker either (im a hong konger/vietnamese) & these tips are what i've learned in the past & since u need help...im sharin em xD

Hello there :)) Is it your first time writing or is it just your first fanfic? If it's your first time writing, don't worry. ^^ Writing comes from experience and also from reading a lot. By doing these two things frequently you'll find your own writing technique. A beta reader can help but I think before that you should get comfortable with what you write and the content should satisfy you. Don't worry about the grammar thing too. It will be understandable even though it has mistakes. I mean, I'm not a native speaker too but it has worked out for me. Also, writing in english will improve your language skills. Uhm... I actually have a bunch of writing tips I can give you.
1. If you want to write a multi-chaptered story, first plan it and then write. I can't tell you how many times I had to stop in the middle of writing something and ask myself "Ermm.. now what...?"
2. Try not the repeat the same word within a sentence, sometimes even within the same paragraph. Synonyms are great! :D
3. Try to make your descriptions more vivid. Like, it is more impactful to say that "The color of blood was decorating her shirt." rather than "Her shirt was red."
It's all I can think of now. I hope I didn't sound cocky, giving advice and all. I just get really excited about writing. Since it's my favorite thing to do... ever. :D
Good luck ^^ I'm looking forward to read your story :))

I second the beta reader idea.
Also, don't be too hard on yourself. You learn from experience. Your first work might not turn out as you want but with each work you'll improve ^^
Most important, have fun :D Good luck ^^

You could try to fine a beta reader.