I have another answer, earlier, about motivations. I am not combining this one into it, because it answers the question more literally.
The most fundamental advice I can give that I wish I had known, which would have let me write more prolifically and better to start, is that discovery writing (pantsing) can and does work, that you do not have to devise a plot to write a good story, is this:
You do not have to plan what happens throughout the book and then stick to an outline like it is a year long chore.
For me, plot outlines sapped the life out of my story and made for (IMO) bad writing. It wasn't new; characters felt forced and the events felt un-spontaneous. The whole idea of writing a "Hero's Journey" felt like signing up for an interminable, predictable, boring chore.
What I personally enjoy about writing is finding characters as I write, and finding their adventure as I write, and finding the conflicts as I write. They go where they will, they are always in character, there is always cause and effect and it doesn't feel "contrived" or make no sense, neither heroes or villains have to be stupid for the plot to progress: The heroes do the smartest thing they can with their information at hand, the villains also do that, they are both driven to win or die trying, and the story ends up somewhere, at some end-point. It cannot go on forever!
In early days, writing for fun, I was tricked by reading books on how to write that all focused on outlines, character profiles and histories, planning victories and setbacks and twists, and turned writing into a chore as boring as planning how to get materials to a construction site on time in the order they would be needed. Like counting how many 2x4s you need to complete a blueprint. Like programming fifty input screens for a tax program. That turned writing into accounting, balancing the books with debits and credits in character arcs, making sure all the peaks and valleys wove together correctly.
Discovery Writing Works.
A book can start with me imagining ONE character doing ONE cool thing. I can generalize their ability to do that ONE cool thing into a "talent" that leads to a story. I can write that scene, and the obvious aftermath, and that will help me decide who that character is: I don't even have to decide first if she is the hero or villain or something in-between; I write what she does and find out.
I admit that discovery writing can demand (for me) throwing out beginnings, throwing out scenes I have written and rewritten several times, changing the plot to avoid dead ends or premature endings, and other wastes of time.
I have read that Plodders (oops, I meant Plotters) have trouble with the middle, Discovery writers sail through the middles but tend to have trouble with endings. I find this to be true, as a result I always have a detailed "description" (not an outline) of the ending of whatever story I am writing, which I revise when it no longer becomes tenable. In my last story I had three different endings, and each time I decided to change, I went through the whole story and double-checked and revised as need to make sure the new ending would still fit.
So although I am improvising my scenes as I go, I am writing toward an ending that ties up all loose ends, reveals whatever mysteries need to be revealed, and fulfill all the "promises" I made in the story. But that is a secondary piece of advice I offer to solve a problem in discovery writing. So is the idea of writing to see if it works while being perfectly willing to throw it away. The most important piece of practical advice is this:
Do not be daunted that nearly all advice on writing is essentially for plodders. Discovery writers are a minority, but it works. It flows better with continuous and plausible cause-and-effect from end to end, because everything you wrote was Domino A falling to knock over Domino B. It makes some of the best-selling fiction on the market.
You can get much great advice from books on writing, especially on conveying emotions, putting characters in trouble, writing dialogue, foreshadowing (for me in revisions after I've written the events to be foreshadowed), and even books on plotting and three act (or Shakespearean five act) structure can help you revise and tune up whatever plot you discovered.
Just don't let those books dictate the order in which you use them: You can write now and apply advice on plotting, dialogue, pacing and foreshadowing later to make what you wrote better.