I think probably the most important part of a story is good characters. If you have engaging characters, then the audience will follow them even through a couple plot issues. Whereas if you have a flawless plot but no one cares about the characters, it can be hard to draw readers in. Not impossible, granted, but for me, if I don't have characters that I find engaging, I think that hinders my stories.
So some people are able to read books and say "Oh, this author did this so well! I'm going to do that too!" But for me, it's usually easier to figure out what doesn't work, than what works.
I picked up the 1980s book Timescape by Gregory Benford at the VNSA Used Book Sale a few years back, figuring I should buy it since it seemed like a quintessential time travel book and time travel almost always creeps into my stories. Now, do note that an exception to the "characters over plot" idea used to be science fiction, where the science and plot were the story and the characters tended to be weak. (Not sure if that is still true.)
But anyway, by the time I got to the end of Timescape...well, I would have thrown it across the room, except I was in an airplane and there wasn't room.
Now, in fairness, the plot wasn't great either, and I'm not so certain about the science (IMO time travel science is always kind of iffy, and if I recall correctly there wasn't any of the exciting time travel I'd hoped for).
But what I really hated was the characters. Keep in mind this is based on reading a book a few years ago, but these are the two things that STILL stick with me:
Point 1: Most of the characters, even when the story was in the 1960s, I believe it was, used "Christ" (or "Jesus" or maybe both; I forget which) as their curse of choice. For an Evangelical Christian, it's like nails on a chalkboard to read any character using the Lord's name in vain. Some people do say that in real life, true. But in a given crowd, are most people going to use that phrase?
Takeaway: Watch for phrases some readers will find unusual, and make sure every character isn't using that phrase unless there's a compelling reason for it. It can be hard to write individual voices for characters, but make sure they don't all sound like YOU.
Point 2: One of the male characters was so attractive/powerful/seductive/perfect that he seduced practically every woman in the novel. One of the women did finally mock him, which I enjoyed for about a second. But then another character accused the mocker of being gay, and she retorted that no, she was bisexual. So it read like no heterosexual woman could resist this man's charms.
At the end of the novel, this "attractive" character had just gotten over a very severe episode of food poisoning (vomiting and I think he was still thin/weak/sweating). Yet he managed to seduce another main character's wife in his weakened condition.
Takeaway: Do not make your character so supernaturally perfect that the other characters act like puppets around him or her.
Caveats to that:
Point 1: This review claims critics found characterization a strong point in the novel! That could be the attitude of 1980s reviewers, and/or it could be that men liked this "characterization" better than women. (Even the linked reviewer noted that a couple female characters seemed to be discarded once they had served their purpose.)
Point 2: Girls/young women being pursued by multiple guys is popular with teen girls (see Twilight and Anime like Fushigi Yuugi back in the day, maybe even Fruits Basket, etc.). So again, it could be a gender thing, and it's probably not fair to judge a novel pointed at one audience (men) based on the fact that it's not appealing to women. But on the other hand, the ending of Timescape hints that the author wanted the novel to be deep and literary. In my opinion, a general audience novel (OR a literary novel) shouldn't treat one gender pretty much solely as objects throughout.
So no, I didn't like the novel, but I'm both notoriously picky and sensitive to sexism. Hopefully I learned at least a little something from it...though books like this one have taught me that no, it's not always best to just plow on through to the end of the book. If a book's too annoying, sometimes you should just put it down!