Personnally it helped me a lot to look up stuff like storycrafting methods. You don't have to follow them but it can help you reexamine your story with a different lens, see where it follows story structure and where it doesn't,
For exemple in my story, the 5 person main cast and the general vibe of each character was the same, but my pov character came off so unlikable that people just hated them so much they didn't want to read being inside the head of this stuck-up douche. I read the beat sheet in "Save the cat" and that inspired me to push the "save the cat" moment to way earlier in my story, which is when mc meets and instinctively saves mc2 from danger despite posing as a misanthropist. Doing that showed the audience that there was a reason to root for the character because they're not all bad and changed how the character was received.
Also just really attack your story with a barrage of questions. Try and tear it down and see what holds up, then work out how to weave everything together so it all stays sturdy.
Why is this character doing this? What do they want to achieve by doing this? Is that really a credible thing someone would do? Remember that no one ever does something for reasons that seem illogical to them, so "they're just bad" or "they just want to hurt people" doesn't hold up. Why? Why do they want this? What is their reasoning as for why it's ok for them to do it? How does me changing this element of character ripple effect all their relationships?
Is this event too much of a coincidence? What questions does introducing this thing about my world bring up? Am I going to answer them? Should I answer them? When? Does introducing this power/element create a plothole for previous story beats? If I read my story like I don't know what's going to happen does any inconsistency jump out at me?
What is the point of this scene? Does it advance the plot, or characterisation? Can I do both at the same time (yes)? What is my A plot and what are my B plots? Is this really what the characters would focus on in this situation? Where is the tension coming from? Would this be better as subtext? Am I thinking ahead and foreshadowing?
Basically be a child that won't stop answering questions about your book. It can also help to read reviews of other books to see what kind of questions readers ask and when so you can get a feel of what you should be asking yourself. I've given you a short list of the questions you can ask.