I was recently watching a writing review talking about the pacing in the recent Invincible adaptation. One thing that the author of this video pointed out is that when authors are very inexperienced and lack self-confidence in their abilities they have a tendency to try to rush to the parts of the story that they feel are interesting as fast as possible to "get to the good stuff", but in the process ruin any sense of viewer investment in the characters or plot. E.g., in Invincible the big idea was
the setting's equivalent of Superman turning out to be an alien infiltrator from a brutal warrior society who killed the setting's equivalent of the Justice League, and his son having to fight against him to protect the planet.
The buildup to this in the comics ends up being very rushed, with the story getting to these "big ideas" by issues #7 and #12 out of ~140 or so (e.g., the deaths of the Guardians of the Globe have little emotional meaning for the reader), but in the process skipping over a lot of important character development and worldbuilding, which the animated series rectified somewhat. The author of the video specifically used Invincible as an example because Robert Kirkman, the author of Invincible, was also the producer of the television show, and it's possible to see how the creator's greater experience in storytelling between the older comic and the much later television show resulted in a less rushed plot.
The author of the video mentioned this issue of inexperienced writers rushing to "get to the good stuff" happens a lot, including with his own work, and it's something I had noticed in my own writing even before watching the video. In my story, I noticed I wanted to really "get to the good stuff", specifically the character interaction between the two leads in a starcrossed lovers plot in an urban fantasy setting. However, in order to orient the reader I had to do so much legwork to establish the setting and characters (especially as the setting isn't a paint-by-numbers urban fantasy with vampires, werewolves, mages, etc., so there is no easy background to explain things to readers). As a result it felt like I was sprinting through the first half of the book, killing off most of the interesting secondary villains in the process. The problem was that with the current pacing the two romantic leads didn't even meet until halfway through the book, which felt like too little time for them to establish believable chemistry. Especially because it results in the first half of the book taking place over a month but the second half taking place over two and a half, but it feels reversed due to pacing issues. But at the same time, because of this sprinting a lot of the tension in the book burned out early (e.g., by the time the leads meet all of the interesting secondary villains had been killed off), and I had a whole list of potentially interesting plot hooks that never got fully explored to "get to the good stuff".
A good example of this is the fact that the monsters in the story, which at the start are treated like feral animals, were once humans and some of them retain some degree of sapience. This is treated as some shocking revelation, but it's been treated as a twist so many other times in other works I thought it wouldn't be interesting to the readers (not to mention antagonists that can't talk or plan are very limited in how they can provoke character development or interaction), so I stuck that about 1/5 of the way through the story. I had to get that out of the way in order to introduce the deuteragonist and villains, who were intelligent members of these monsters, and then get that out of the way so both the protagonist and deuteragonist are established yet give them time to meet and interact. But at the same time my beta readers have told me things like "it would really help if you spaced the reveal out and showed rather than told how the setting worked bit by bit, though doing that made things feel bloated and as if I was adding a bunch of filler that didn't advance the plot in the name of worldbuilding.
The question is for an inexperienced writer that doesn't have confidence in their ability to write, what should somebody do in order to determine the appropriate amount of pacing to add to avoid "rushing to the good stuff" or its opposite? I.e., how do you determine how much padding is needed to make the story resonate, and what scenes need to be present and which don't? In my case, it's very clear there is a problem, but how to go about fixing it isn't clear (and I am aware of the old saying "your reviewers are probably right if they tell you there is a problem, but they won't be able to tell you the best way to fix it"). Obviously one answer to this question is "get more experience as a writer to figure out how much pacing is appropriate", but this feels kind of like putting the cart before the horse when one is trying to figure out at least a loose idea of how to pace the story. "Just wing it, hope for the best, and learn from your mistakes" doesn't seem like a very workable way to plan a story.
EDIT: To clarify, I'm not saying that the idea that more experience as a writer would help the problem is incorrect, rather that it's a passive solution that I cannot actively pursue when trying to figure out best practices for revising the story I have right now. Greater experience will definitely help whatever I work on far in the future, but it isn't applicable to aiding in revising a manuscript in the present.