However...the writing world is not filled with "most people." It is filled with pedants, folks who choose language as their method of feeling superior to others, and the exceptionally well read who are tired of watching the jocks get the hot girls and have chosen word nerdery as their elitism of choice.
Writers who wants to be taken seriously must be aware of gatekeepers who do care about the "right" way to use words. Someone may represent them (or not) or publish them (or not) based on their "proper" use of words. Self-publication is no escape, as many will gleefully castigate a writer just for the glory and honor of being seen doing so or even simply for the pedantic bliss.
How it's often used: Unimpressed or unaffected. (I tried to appear as nonplussed as possible by the fact that Jeffery turned into a werewolf over tea and scones, but beneath the table I was wetting myself.)
What a writer should know: Nonplussed traditionally means confused. (I was nonplussed at the funeral because I was still wondering how the hell someone could die from asparagus pudding.) Someone who is bewildered or overwhelmed by information. They are at a loss. The facial expressions of someone who is completely overwhelmed and confused can seem almost neutral compared to a situation's emotional urgency.
How it's often used: Useless or unable to perform. (The information from the security company about the ground floor security mechanisms was redundant since we would be coming in from the roof.)
What a writer should know: Redundant has to do with a surplus of something that is not needed; usually a repetition. (The information from the security company about the ground floor security mechanisms was redundant since we had already gotten it through surveillance the week before.) While redundant information or equipment might be useless, not all useless information or equipment is redundant.
How it's often used: An abundance. A lot. (Jefe, would you say I have a plethora of pinatas?)
What a writer should know: Plethora classically goes beyond an abundance. It means a large excess. Way way more than is needed. Too much/many. (The plethora of pizza for the party ended up going home with Chris who guiltily ate it, despite self loathing over his weight.)
How it's often used: Reluctant. Unwilling. (Billy was extremely reticent when the instructor asked him to put his answer on the board.)
What a writer should know: Traditionally reticent only has to do with being unwilling to speak. Very quiet people are reticent, but they may not have any trouble writing on a board and aren't necessarily shy. (Billy was reticent about reading his answer to the class because he hated his own voice.)
How it's often used: As a "highbrow" way of saying amused. (The crowd was filled with bemused faces at the young child's tap dancing prowess.)
What a writer should know: Bemused's more standard definition is to be confused, befuddled, or lost in thought. Bemused faces wouldn't know what the heck they were looking at. (The crowd was filled with bemused faces at the young child's rendition of Sweeny Todd's God That's Good.)
How it's often used: The really, really ultimate. Extra ultimate with ultimate sauce. (It was my penultimate achievement to have a foursome with three other women who were all way into me and each other.)
What a writer should know: The confusion here starts with "ultimate." Ultimate is usually used to mean "best." This definition is actually so widespread that it probably won't get you into trouble and is generally considered acceptable even among the pedantic, but back in the day, "ultimate" really only meant the last in a series. It's more modern usage as fundamental or greatest is a later development. PENULTIMATE in standard usage actually means the second to last. (All the surprises happened in the penultimate chapter. The final chapter was just a denouement.)
How it's often used: Any sort of coincidence that is amusing. (Isn't it ironic that it is raining on your wedding day?)
What a writer should know: Irony doesn't refer to any unfortunate circumstance. However, typically this rebuke about the misuse of "irony" comes with a definition like "when the outcome is the opposite of expected." (It is ironic that Alanis Morissette's song irony contains few examples of actual irony.) But a writer should be aware of the meaning of the word beyond just the meaning that sticks it to pop artists. Tragic irony, cosmic irony, dramatic irony, situational irony, and verbal irony are all different things, and you're going to look JUST. AS. FOOLISH. if you go around saying there are absolutely no examples of irony in Alanis Morissette's song. In fact, the verse about the guy in the plane is TOTALLY an example of irony, not just of situational irony because he was afraid of planes and died on his first flight, but also verbal irony when he said "Well isn't that nice."
How it's often used: Not interested. Lacking interest. Uninterested. (I was disinterested in the sex life of old people.)
What a writer should know: Traditionally disinterested actually means having no opinion on a matter. You could find a debate extremely interesting but if you don't lean toward one side or another, you would be disinterested. (I was disinterested in the outcome of the debate on nanotechnology even though the entire subject is fascinating to me.)
How it's often used: Utterly destroyed. Wiped out. (The relatively low crime of Oakland was decimated by the arrival of crack cocaine in the eighties.)
What a writer should know: This one didn't used to be a big deal and its "misuse" is extremely common--even, arguably, more well known than its proper use. It may even bring into question what the hell it means to be "right" about a prescriptive foible when it hinders communication with most people. But in the last decade or so, it has really come into vogue as a chic way to be prescriptive. All the cool pedants know the "real" meaning of decimate (and correct everyone else about it like insufferable shitheads).
Decimate is a word from Roman legions which referred to the practice of killing every tenth soldier (usually as punishment for losing a battle--and you thought your boss was annoying). Deci=ten. So decimate traditionally means only to reduce by 1/10 and not to totally destroy. (After the crushing defeat at Rhone River, Caesar ordered the general in charge be killed and the men to be decimated.) Good luck finding the instance when it is actually appropriate to use this word "properly." Hail Caesar.
10-Literally (this is literally the one to be the most aware of)
How it's often used: As an intensifier like "really." (He was literally as big as a house.)
What a writer should know: Literally traditionally means an actual, literal truth. There is no exaggeration, hyperbole, metaphor, personification, or any other use of language but objective and absolutely denotative. The words described by "literally" should have no figurative meaning whatsoever.
Misuse of literally is one of the single biggest no-no's you can make right now. It has become the pet peeve that everyone loves to hate. There are t-shirts, coffee cups, and thousands of web pages and youtube videos dedicated to hating the misuses of this word, as well as mocking and deriding those who get it wrong, impugning everything from their breeding to their intelligence to their eduction, and even their morality based on this single misstep.
(Using "literally" before hyperbole is literally one of the worst mistakes you can make as a writer in today's world.)
Walk out into the world, and people use words the way they've heard them used. That's what language is. That's how it works. That's how our brains evolved to communicate using sounds and symbols. Telling people they are "wrong" about language is at best as futile (and often as unwelcome) as telling them they are "just wrong" about their preference of food or clothing style.
At worst it's kind of classist and (if they're using a dialect) probably racist.
So if you want to be like my step-father and delight in correcting people's grammar and vocabulary, just know that will probably end up with his reputation for being insufferably arrogant (even among the other faculty), and like him, you will probably die alone, surrounded by cold tweed and unloving fuzzy sweaters.
The good news is that these days you probably don't have to worry about the difference between "making" money instead of "earning" it or how dreadfully uncouth it is to have your protagonist "climb down" something. I think the ghost of Ambrose Bierce even stopped manifesting over the "like" and "as" debacle. And not every word carries the same kinds of stigmas as the ones above do. For example, using "refute" instead of "rebut" is considered a mistake, but it doesn't typically lead to the eye-rolling conclusion that one doesn't know how to write the way a misplaced decimate might. And the really good news is that people outside these priggish circles of judgmental pedantry will seldom split hairs with such glee.
But it is the people within these circles a writer must most often impress. They are the gatekeepers and the avid readers. They are the serial commenters and the linguistic well actualista. They are judging you--sometimes quietly, often vociferously on your usage of a few key words that they deem to be bellwethers of proper language and their usage to be the "correct" form. And if you could work around them, I'd tell you to, but life is going to be SO much easier if you just figure out what they're on about.
Besides, it's not like they're wrong. They just need to get fucking laid or something.