-Accepted Creepy Knoweldge. Because finding out someone has been secretly watching you and your friends for years, possible part of the future as well, is not creepy at all. Even if they don't get any intimate moments, well, you still are going to think Stalker, Spy, or something equally damning. Or I suppose they might try to pass themselves off as a seer, but that rarely happens.
~A subset of this is that people who know of a world as fictional don't actually have to explain it as such. Personally, I would explain it like this.

"Are you familiar with Seers, prophecies, or similar? Well, back on my world/dimension/reality, there is at minimum one, probably many more. Somehow, they are able to peer into other worlds, and possible other time. They see the stuff going on there, and write stories about it. This world is one of them. I already know a lot about it from those stories."

-Straw Vulcan. Because logic doesn't work that way. At all. Nor does anyone worthy of a character slot act that way unless in jest.

-Failure to actually use SCIENCE properly. Proper SCIENCE follows the SCIENCEtific method or something close, rather than, well, what Hollywood has deluded everyone else into thinking it is.
~Real scientists, on confronted with magic, will be Sceptical and disbelieving, up until someone starts levitating things. Then, after they make sure it isn't a cheap trick via transparent wires, they will try to figure out how to reproduce it. Eventually you end up with Tractor beams on your Starship.
~Arcane Howitzer had the guys from HALO carving Eldrich Runes onto their starships because, although they had no idea why it worked, it did in fact result in a hull plate with energy shielding. Hollywood has scientists going "This is Impossible, and gettings Logic bombed.
~Magic users are rarely better. They usually have no useful information on how magic works either. Admittedly, if you are gifted magic, or born with the easy version, instead of figuring it out yourself, with you having to know exactly how it works to use it would problems, It is understandable.

"I am having trouble discerning the real from mere folklore, superstition, and outright scams," the doctor admitted. "Could you perhaps assist me with that?"

"Me?" Sailor Moon pointed at herself. The sheer amount of books in the room was rather intimidating. "I only use magic," she said quickly. "I don't actually know how it works! I say the spell, something happens!"

Dr Mizuno frowned. "In that case, I would like to talk at some point to the person who taught you.

- MLP Specific
-Foalish. In the Pilot, Nightmare Moon uses the term repeatedly. All fanfictions I am aware of that use the term, use it to replace the word Foolish. However, I believe this to be in error.
There are many, many immortals in fiction. Most of them are Arrogant and see Mortals as lesser existences, to the point of classifying them as similar to bugs. Interactions often end up with Immortals calling Mortals various things, including Children/Child.
Nightmare moon, Like celestia is extremely long lived, if not ageless/immortal. This suggests that Foalish is actually analogous to Childish. As in Childish behavior would be called foalish behavior, as in behavior a foal would do.

-Violence Aversion
Aside from Fluttershy, the rest of the Main six are fully willing to use violence in the show. However, many fanfictions have them all be horrified by the idea of violence. And this is thier normal state, not while corrupted by discord or similar.

~All of them, save fluttershy fought the changelings, and with little hesitation.
~Rainbow dash, well, violence is pretty much her first response.
~Rarity, During the Pilot episode, she was the first one to attack the manticore.
~Applejack used what would probably classify as lethal force against the timberwolves.
~Pinkie Pie I can only think of her using the Party cannon against the changelings.
~Twilight. Well, I seem to recall, after Tirek destroyed the library, she went into rage mode, and started throwing nuclear-yield blasts at him. Repeatedly.

-Meat Aversion. Plenty of fanfictions suggest that Ponies are horrified at the simple idea of an omnivore eating meat. Also, they tend to inaccurately call them carnivores. This is most commonly seen from Fluttershy.

However, In the show, Fluttershy specifically feeds some of her animal friends fish. That makes it pretty clear that there is no way she would have a massive aversion to the idea of eating meat.
Rainbow dash is secondary, since, as a friend of a Griffin, who are always either carnivores or omnivores (Cake + train episode suggests second option) there is no way she doesn't know Gilda ate meat.
On the upside, some stories have fluttershy casually noting that a human is an omnivore, just by glancing at their teeth. Well within what she should be capable of.

https://www.fanfiction.net/u/2269863/Less-Wrong
Rule One: If you do anything to increase the protagonist's power, or make their life easier, you must also amplify their opponent or add extra difficulties to their life.

While not entirely accurate, it certainly seems like a good guideline.
As far I am concerned, a story, fanfiction or not, either needs conflict, interesting situations, or excessive (and effective) humour.
Without conflict, most stories don't work. But, if the story is slice of life, the conflict might be really minor, and it is more that the story does worldbuilding, and lets you experience that life. But it has to be done really well, or it won't work.
Alternatively, you can have humorous stories. they generally need to be really short, or else need to be sufficiently ridiculous "Crackfics" such that the reason you read them is to experience uncontrollable laughter. Due to how massively subjective humor can be, this may not be as reliable, but when it works, it is great.

Rule Two: Originality isn't easy, but it is simple: Just don't do stuff that's already been done.
Given how many stories follow the exact same path as canon, often with a buffed protagonist negating the conflict and challenge, its not surprising that the few that entirely derail the original storyline, or throw massive curveballs are fascinating. This is even more important for Self Insert, (Meaning here, a person who read the story or watched the movie before entering the world) since if they already know what will happen, and you don't either apply the butterfly effect, cause their actions to cause things to spin out of control, or just make things different enough to throw them off, the conflict is gone, and so you have to use of the other two options.

Rule Three: The premise of a story is a conflict and its resolution
For Conflict based stories, yes. And having an idea of what the conflict is, how it got worse to handle the protagonist's increased power, and how it will be resolved seems quite important.
As fanfiction, it is really important to increase challenges proportional to how much stronger the protagonist was than the original one.
A Self insert might have foreknowledge, but you can use broad strokes, declaring that the overall story is the same, but details are different. Or their interactions happen to eventually ruin split second timings that are often critical in the original material.

So while yes, these rules are kinda accurate, its a bit more complex than that.