There are many ways writers can go overboard, taking a basic idea or theme and focusing on it to counterproductive levels. Just like infodumps are in large part world-building taken to extremes in the finished narrative, it's possible to caricaturize voice, alliteration, characterization, or any other technique. It's hard to call these "mistakes," per se, because everyone has different tastes and some people approach reading the same way they approach movie nights.
That said, there are Army of Darkness caliber B movies, and Manos: The Hands of Fate caliber B movies, and it's good to at least be aware of these things.
After learning about diction, some people get stuck there for a while. An elephant can't simply be large. It has to be hulking, immense or nigh omnipresent. Similarly, a villain can't be evil nor a runner quick, not when they can be dastardly and incorrigible or swift and Mercurial (pun intended).
It's good to experiment with words, but at times that experimentation can take over, which is why simple language often works best.
Grandiloquence or Purple Prose
Purple prose is one part thesaurus dropping, one part drama queen and one part artiste. Some people enjoying playing with language so much so that their writing gets tinged with self-important douche. If it's not over-exaggeration, it's a needlessly bombastic analogy or an obscure mythological reference, all tied together with a sense of Destiny! (For some reason, appositives seem to pop up a lot too.)
My tantalizing prize, so long aloof yet so present and so near, taunted me like the memory of a lost lover whispering your name in supernal satisfaction. This empyreal vision of delights promised and foretold spoke to some chthonic longing and I, Sisyphus denied, could but watch as my mind, unbidden, forged fantasies of vengeance from burning shards of discontent.
A man's urges, forever skulking at the edges of civilized restraint, flame malevolent when thwarted and despite the omnipresent opprobrium of society, I found myself compelled to action.
Dude. Calm down. Vending machines do that sometimes, and just because the fruit snacks you want are hanging off the spiral coil, that's not worth tipping the damn thing over. Even if it was your last $1.50 before payday.
It's a shame, too. Purple prose is my favorite mistake and, while it can be useful for satire, I don't get to write it nearly as much as I'd like. Unless you're going for humor, you really need to stop before your story sounds like "What I Did on My Summer Vacation," as narrated by Invader Zim.
One of the reasons prose writers should learn meter is to avoid metrical hijacking. That's when a group of sentences fall into a metrical pattern for long enough people get sucked into the meter and drawn away from the story. If a story or poem sounds "sing-song," most often the meter's hijacked it.
An example of mine is from "The Festival of Flame" in Gears and Levers 1. The last three paragraphs (spoiler alert) read:
As he died, Fa Xui watched the growing flames, felt their heat. The walls of the church faded away and then he was in the air, looking down.
The church was on fire. With all the red lanterns, Beijing was on fire. The lights on the ships in the harbor, European and Asian alike, were also flames.
Above, the stars were clearer and brighter than he ever remembered as they slowly faded away.
The penultimate paragraph is just about on the edge for me with regard to metrical hijacking. While the surrounding paragraphs are relatively unmetered, it's dactyllic with flanking unstressed beats and some caesuras (stressed syllables are highlighted):
The church was on fire
With all the red lanterns,
Beijing was on fire.
The lights on the ships in the harbor
European and Asian alike,
The editor, Phyllis Irene Radford, suggested making the last phrase "were also in flames," but that would also make it dactyllic:
were also in flames.
For me, an entire paragraph of rough dactyllic meter when nothing else in the story was especially metrical was too much, especially since dactyls can gallop off on you if you're not careful. I preferred the iambic "were also flames" as a way to slow it down as a transition to the non-metered close, and she was kind enough to accommodate me.
The Invincible Hero/Over 9000
It's natural to want your characters to be unique, exciting and even powerful, but taken to extreme it can start to ring false. In some works, people can't be normal or average or anything less than elite.
They can't be a competent bodyguard. They have to have been at the top of their class in bodyguard school as well as still bearing the scars from where they personally saved the life of the Generalissimo of the Interplanetary Badass Confederation.
Their travelling companion isn't an average magic user; they have untapped depths of hidden potential that amaze the few able to sense them.
And the barkeeper at their favorite bar is actually an ex-special operative whose existence is so classified he has implants in his brain so that even he doesn't remember everything he's done.
Characters need flaws and limitations to be believable and interesting, and if everyone's an invincible hero or their power level is secretly over 9000, it gets old pretty fast.
The Google Says
TV Tropes - I was going to try to come up with more, but just about all the ways to go overboard can be found here. The question isn't whether the tropes are present (because they're the basis of what stories are built from), but whether they're handled with skill and grace.