The easiest way is to Keep doing it! Even if you dont consciously try to “get better”, youll find that just by the act of writing youll gradually become better at it… But. If you actively want to improve, you cant do it on your own

1. You can go out and find resources! I dont know your experience level or anything but a lot of fic writers are hobbyists without prior education in writing (and often dont even have english as their first language) and could really benefit from really basic writing and creative writing advice that can be found on youtube!!
   Heres some random videos on some basic writing things:
   How to do dialogue tags: https://www.youtube.com/watch?v=PZ3wz-cDtS8
   Filter words: https://www.youtube.com/watch?v=5JrQGZzPUxE
   Bunch of different things: https://www.youtube.com/watch?v=N70D6xP0aQo
   How to avoid epithets: https://www.youtube.com/watch?v=UmAeAt-gdRU
   And obv take any advice with a grain of salt and dont have those introduction videos be the only ones you consume.. Let your curiosity guide you and go deep dive into the technicals of writing!! But those 4 really cover a big area of things fic writers can improve on! Theres also many more lessons you can find on youtube.. About storytelling and creating characters etc.. i really recommend diving into different writings too. Like. watching videos on advice on how to write poetry or song lyric or how to write screen plays! Lots to be learned from those too…
   And with all that newfound knowledge you can go back to reading books and fics and really understanding why certain sentences and techniques work for you.. And then you can apply all those to your own writing too !! profit

2. If you want to get better then im afraid theres no way around getting feedback from other writers. This is THE number one thing in how to get better. Your own perception of your writing is incredibly biased, and only when you see it through someone elses eyes do your little quirks really sink in… so.. Its helpful to find someone whos passionate about writing and improving, and letting them give you honest feedback !! thats a whole other hurdle obviously because youll have to Find Someone that you click with and then be vulnerable enough to let them go ham on your writing (and also offer you just as much praise to balance it out too!)
   ALSO alternatively if youre too vulnerable to find a beta for your own work, go be the beta for friends who let you go use their fics as a sandbox!! Im forever grateful to my friends because every time i beta i offer a Full Pakage where i give them All my thoughts. All of them. That often means leaving a suggestion or how to rephrase something every single paragraph (so basically like an editor) . its kind of intense and this does Not work for everyone (because a lot of people dont want that type of honest feedback AND its a lot of work for yourself too so you have to be passionate or a little insane)!! but it helps me a lot because figuring out “what doesnt work” in others writing and suggesting an improvement is wayyyy easier than doing your own stuff that youve reread a billion million times. It also forces you to Explain why you think a sentence would work better differently (because i think its rude to suggest to rephrase something without explaining why) so it really helps you nurture your skills without actively doing your own writing.. I love betaing..

Okay… thats about all i have to say without more specific details..

And i will also say: please listen to none of this advice if youre currently in a writers block. Im being so serious right now. No amount of improvement will help you through a writers block . writers block isnt a disease of Skill, its a disease of the Mind where anything you do feels and sounds bad to you !!!!! And if you then go and learn all these fresh writing skills and go back to your doc that you hate so much, youll now only have gotten BETTEr at pinpointing your mistakes and hating your writing (with slightly more ValidTM reasons this time)!! And thats NOT what we want.. No new knowledge for you if youre only going to use it to hate yourself….!!!!!! Only go seek out new knowledge if youre curious about writing as an artform and want to understand why you love the things that you love and become better at giving positive feedback and become more appreciative of the skills and quirks that you (or your friends) already have naturally.. I mean new knowledge might also help you get excited about writing again but… but just trust yourself and dont go deep dive into “improvement” for the wrong reasons…..
(also if youre wondering how to get over a writers block, its basically the same way you get over a bad mental health episode. Its highly personal to you and you have to figure it out for yourself sorry (but also: the solution is walks. Take so many walks !!!!! and also listen to music and also do other forms of art))

ALrIGHT thats it now psa over thank you for asking and i beg you to not take anything i say as serious ever. Im just a guy on the internet who knows nothing. Thank you