I am a discovery writer. I recommend it highly.
For me, I begin with a character. All my characters have something "special" about them, something they are good at, as well as a flaw, often something they are not good at, and will need to get around or overcome.
Then I start putting them into "throwaway" conflict situations, which I write out, in novel form; editing and tweaking as I go. By "throwaway" I mean conflicts that won't necessarily be part of a plot or part of the book, it is just waking up with the power out; or not being able to start the car. Or their phone that they rely on heavily is suddenly dead. Basically they have some problem from their everyday life and have to solve it, so how do they do it?
For me, this helps define their setting and time, their relationships, their job, and their personality. Their "normal world". The story is going to be about this character dealing with problems, they need to be proactive and search for ways to do that. In the end it is these "throwaway" problems that will tell me what the BIG story-driving problem is going to be.
I am still not "plotting". But the goal is to find a character I find compelling, make her human, understand her normal world, and then give her a problem to solve that will change her life.
I do the same with any main characters she will meet or team up with along the way, although they will not necessarily have a life-changing problem to solve (they might, if she is saving the world, but also may just be helping her achieve her goal without changing their own lives).
If you have characters that feel real to you, and you don't let your hero stall on the problem, then the story will turn out somewhere. You don't need a plot, you need your character to have a single-minded focus on pursuing a solution to the problem, and effecting non-neutral change, what she does results in setbacks or advances, nothing neutral.
Pick your scenes so that nothing happens in a chapter that can be undone, for example, do not write chapter 7 in a way that chapter 8 can nullify chapter 7, and leave the story back at the end of chapter 6! What happens in each chapter should change her knowledge, a relationship, the situation, who is alive or dead, who is a friend or foe, irrevocably. Doing that, the story has to come out somewhere!
I only write book length stories. The greatest problem discovery writers have is with endings. The rest is easy, I don't "force" my characters into a plot. Similar to real-life friends, I have built up a "mental model" of how my characters will behave in various situations: They do what they would do. Let the chips fall where they may.
Getting to an ending: I generally have a specific ending in mind, and I keep notes on how the story could probably end, and why.
If I write a chapter, and in the process of keeping my characters true to themselves something happens that rules out the ending I had in mind, I have to come up with a new ending, at least as good. Preferably even better. If I cannot for the life of me see how to do that, I have to scrap the chapter and come up with something else; or find a way to change it that still has my characters acting consistently but making a different decision, or with a plausible but innocuous chance change in circumstances, that preserves the original ending idea. I do find new and better endings frequently, often two or three times in the course of writing.
That is my advice. If you Google "Discovery Writing" you can learn more about how this technique is accomplished. Stephen King and many others are discovery writers; aka "pantsers", meaning they write by the seat of their pants and make stuff up as they go along. I would compare that to "plodders" or "outliners" that try to figure out their whole story in outline form and then stick to it.
Even if you ARE a plotter, taking this approach to starting a book, with a strong character you have developed by writing scenes, may trigger an idea for a complete plot you can outline and want to write with this character. Nothing says you have to be one or the other; many authors hybridize these two approaches to meet somewhere in the middle.