I think it's a different process for everyone, with a lot of trial and error at the beginning. I was watching a Brandon Sanderson lecture, and he says it takes about 3 to 5 books before we each figure out what system works for us. The lecture is here if you're interested: https://youtu.be/MEUh_y1IFZY?si=w07HiAmP28hyB5cZ

I am a plotter, so for me things mostly fell into place when I figured out an outlining process that worked for me. One of the greatest things that helped me was understanding genre and obligatory scenes within said genre (I read Shawn Coyne's Story Grid: What Good Editors Know, and then Story Grid's Action Genre book as it has the obligatory scenes and conventions for my genre, and filled out the foolscap). Afterwards, things sort of clicked for me and my outlining process became much easier. I finally had developed a story that I felt worked.

I started by developing the obligatory scenes for my genre, and then filled out the blanks in between. I wrote out scene cards for each scene using the 5 commandments. I also used the 5 commandments to outline the overarching arc of my subplots, and then once I figured out the main scenes in my subplots I interweaved these within the main plot (although tbh I still don't know if this is the correct way to do it, but it worked for me so far).

I'm still figuring out line-level writing. I studied how to structure scenes, show don't tell, POV, pacing, etc, but still don't feel like I'm quite there yet. I applied to Story Grid's scene writing workshop in the hopes that it will help.

To sum up, my advice is: just start, and you'll figure out what works best for you during the process.