I think it can be hard to pinpoint exactly what is holding our writing back. For a long time, my biggest problem was sticking to the present narrative. I would sometimes go off in another direction for too long which only hurt my story. Now that I'm aware of this I often have to remind myself that this is a problem for me and be on the lookout so I can catch myself doing this. Part of the problem was that the writing wasn't bad when I did this. Maybe it's even good writing, but it was hurting me in the big picture. I still catch myself doing this at times, but I'm quick to realize it and get myself back on track. And what a difference it makes to really stay close and focused on the present narrative of a story. Has anyone else had trouble with sticking to the present narrative? I do still see it as a challenge.
This may sound silly, but the scenes I find I am happiest with, and flow onto the page the easiest are the ones I can see in my mind, like watching a clip from a movie. Trying to go to sleep the other night, I could see a scene playing out. A conversation between two of my characters. One is a farm boy, never been more than 10 miles from home, the other is his mentor. The conversation started with the boy commenting that people in the area they were traveling through talked funny. The mentor went into a bit about dialects. Then it came back around to the plot. I used it as a way for the boy to open a different conversation. That little side trip seemed to make the whole thing work. just my .00002 cents, as adjusted for inflation.
The present narrative is the actual story. The plot that is currently unfolding. Flashbacks, descriptions and things like that step outside the current narrative. And, of course, that's something that happens, but you don't want to leave the current narrative for too long at a time. Vonnegut said Esch sentence should either advance the plot or reveal character. The present narrative is where you advance the plot. When I've stayed from the present narrative for too long it can be hard to get back to it and find my foothold. I'm learning to sprinkle in the details that aren't part of advancing the plot in a way that they are so blended you don't really notice Tham as there own thing. Well, that's the idea, anyway.
Even with something like breaking away from a dialogue for a moment to reveal the POV character's thoughts or feelings, I find I have to keep it really brief or it breaks the flow of the dialogue. No more than one sentence or maybe two really brief ones usually. At the end of a dialogue I can go deeper into thoughts and feelings, but not during. It needs to be just brief hints.