My speaking only got better after speaking a lot with native speakers, just, a lot. And focusing hard on vowel sounds. In Norwegian specifically those kill a lot of understanding. If you can't immerse by living there, I really liked 1:1 online interactions. I paid for an italki instructor my first year here.

My writing is still my weakest point. I'm fine with spell check and predictive text on my phone, but my spelling is atrocious without it. That could be improved with spelling practice like we did as kids in our native language, but I just haven't put in the time, due to how common spell check is.

Basically just time and effort! Sorry, I know it's not a nice answer. It's just a really hard thing to do, and you have to keep doing it, and a lot of people minimize the effort. Maybe it's easier for some but not most of us.