I'm a discovery writer. I provide a lot of detail on beginning a story as a discovery writer, in this answer.
When I began I tried to be a plotter, but it didn't work; my creativity was used up in devising a plot, then it just felt like a job working through the outline; and on top of that, I didn't like my characters, it felt like they couldn't do and say what was 'natural' to them, and they felt like wood puppets. I'd lose interest, the story would stall, and I abandoned three decent story ideas that way.
Then I read Stephen King's "On Writing", and Stephen King is a discovery writer, with a similar problem.
Read my answer at the link above. For me the key is to start with a character, that has a problem. I don't plot out what happens and when, I think about my character for weeks before I start. I think about her problem. I think about her normal world, what she does every day and often how she got there. I don't write all this down anywhere; it is in my head.
Then I come up with a first scene I can use to introduce her, with some minor everyday kind of problem she has to deal with (not her big problem), and I start writing that scene, introducing her, the world, the setting, etc. The first hint of the major problem occurs about 10% to 15% of the way through the story.
I write in keeping with the Three Act Structure, but without plotting it all out: I just know, based on where I am in a story and how much I have written, what type of thing needs to be written next, and that is when I am going to invent that thing: In keeping with my story so far, and my characters so far, I'm not going to force them to act against their personality. The only "forcing" that happens is external events beyond their control; to which they are forced to react. e.g. they may get fired. Or perhaps are present during a bank robbery. Or perhaps her car won't start.
The biggest problem for Discovery writers is typically not the first Act or the Middle, it is bringing all the threads and character arcs to a simultaneous conclusion. So it is the Ending.
This is why you should write with some Ending in mind that will resolve everything; but it is okay to change the ending as long as it remains consistent with what you have written so far (or if it is easy enough to tweak previous scenes to make a better ending possible). Whenever you finish a scene, make sure your ending still fits, or come up with a better ending, or revise the scene you just wrote while it is fresh in your head. I usually change endings a few times in every story, learning about my characters as I go makes me think of more satisfying endings.
Positional awareness is also important; where you ARE in the story. Think of it as deciding to bicycle from Seattle to Miami; but without planning a route. All you have is your phone, and each day you plan a route for biking that brings you physically closer to Miami. You may find this brings you to a river you cannot cross, so you have to find a bridge and doing that may take you further away from Miami temporarily. But after crossing the bridge you can get back on track. Eventually and inevitably you will get to Miami, discovering your route along the way, solving problems along the way.
It is obviously not the most efficient route, but the most efficient route is seldom the most scenic route, or the most fun route. And in a redraft, you can cut superfluous elements that are not that entertaining, or rewrite things that no longer seem to fit the story and characters.