I think honestly the hardest part for me is just getting to know my characters and how how they connect to one another. I've been told my characters are my strong suit, so I really try to delve into them and get to know them on an intimate level. I try to flesh them out so that they have hopes, dreams, goals for themselves.
I learned some things that I hadn't expected and I learned some tips/tricks to be more successful. Overall though, what I learned was applied after the fact, to the editing process.
Just f****** write! I used to think that I wasn't good enough, and it really took nearly twenty years and some amazing friends to convince myself to actually pursue writing and to finish a story.
I started really writing when I was 8 or 9 years old, but never really finished anything. Even into high school, my imposter syndrome was terribly overpowering and a lot of decent stories got the axe because of it.
Just write. Write whatever is floating around in your head, write it out of order, it doesn't matter, just write. Get it on paper (or digital paper) so that it's saved somewhere besides just your mind. Figure out how it goes together later. I try to put an hour each day into my work-in-progress(es) even if it's just brainstorming or fleshing out characters. The more time you spend allowing yourself to explore the universe you created, the more fleshed out the writing will come.
It's such an odd feeling! I actually had this happen at my local post office recently as a matter of fact! I was mailing out some signed copies of my book, First Strike: Zero Dawn and was chatting with the post office clerk. And this guy behind me recognized the name, said he had read and loved the book. It was a very foreign feeling, and I will admit I didn't really know how to handle it. But ultimately, it was a great feeling.