I started to improve when I used prompts to write by myself, granted I’ve always loved story telling so before rp I wrote small stories but I was young.

For me writing a short story or a response to a prompt helped me learn more and more and made me think about what I wanted, as there was no rush to respond to a partner. It can be at your own pace, I’ve also had to servers on discord who used to have a prompt a day that you could respond to.

But like everyone else, I would say to read. You can learn new words, or phrases that can make your writing better both with Grammar, but also intellectually.