New writers are inundated with advice from family, friends, strangers on the internet, and their own brain. You're told to go by the Stephen King method of only using "said" as a dialog tag. You're told to use more descriptive dialog tags. You're told to keep exposition to a minimum. Nope, yet again, be more descriptive. Don't write too much. Every third sentence is probably irrelevant.
When I was starting out, I made lots of mistakes. The very first printed and ebook versions of Order of Vespers were a mess. My title headings were different sizes, my table of contents only sometimes worked, and I had typos that my editor missed. It was a disaster that improved over time. I'm pretty proud of my formatting for The Black Knights that only needed a few changes. Hey, I'm not perfect.
So here's what I wish I knew back then.
Get an established editor. It's worth the money even though it's a pain in the wallet. I learned my lesson the hard way. If you can't afford an editor, invest in ProWritingAid and Grammarly. Use them in addition to spellcheck. Then have someone read it with a keen eye, not a friend who will just tell you that you're wonderful and your work is perfect.
Build a base of regular customers. I relied on my family and friends to buy my books and spread the word to others. That worked for the initial sales of my first book, but it definitely faded over time. I did well selling my books at comic conventions, and people returned year after year to buy the newest book in the series or just to talk writing, it didn't translate into those first-week sales that everyone wants. My advice: create social media accounts before you release your book. Look at some successful authors' pages for ideas. Since you might not have a cover or concept art, you can post about yourself, your process, your laptop, etc. Connect with people online so they will also buy your books. Network with other authors. Join Facebook groups that connect readers and writers. There's so much more I can say, but those are the key ones.
It's okay to cry. I thought I was a freak of nature because I cried every time I hit a roadblock in the writing process. Order of Vespers was such an emotional process. I pantsed the entire thing - wrote by the seat of my pants with no outline - so when I got stuck, it was not an easy thing to work my way out. As I met more writers, I learned that I wasn't the only one who goes through phases in the writing process. Not everyone cries. Some people curse their characters. Others stop writing for a while before returning to their work. It's okay to get angry, sad, or excited, or all of them at the same time. Writing is a tough, solitary process, so do what you need to do to get that book done. Obviously, don't destroy your mental health in the process, but allow yourself to have feelings about your work.
There are other lessons like don't trust every offer you get, submit and host panels at writing events, expanding past book fairs, etc, but I don't have the energy and you probably don't have the brain bandwidth after reading this post to get into it. Maybe another day.
What do you wish you'd known before starting your writing journey?
Also, this is not my dog. I just like the sad puppy eyes because it encapsulates exactly how I felt when I realized all the things I did wrong.