Alright, I won't go into the specifics here because I don't really like telling people how to write. Now before anyone starts flaming me for being hypocritical, let me clarify I do NOT mean the style.
I'm referring to what happens behind the scenes, the outlines, the plot conceptions, the character profiles, or even the lack thereof.
If the writing style one uses to convey their story is how they talk (accent, language, word choice, etc.), then the process behind it is akin to them thinking about what to say. And I don't really like telling peeps what to think.
Anywho, this will just be an overview and such. This section is the same for pantsers (those who don't think and just write what comes to mind) and those who outline everything or just partial outlines.
Having a good foundation in the story is HIGHLY recommended. It makes things so much easier for when you're writing a few hundred chapters in. Without the good foundation, then there'd be some plot holes that could creep up unnoticed until it's too late (another reason why editing is a must).
The "foundation" is NOT the early chapters. It is the power system, the basic worldbuilding of the first setting and with open ends to possible connecting settings, the mc's personality, the personalities of those around him, societal norms, etc.
If you have trouble identifying traits of the foundation or you're not sure if you're missing something, just refer to real life.
This example takes an aspect we consider to be common sense today, then relates to the story's setting and fleshes out the details. One method of having a good foundation is to flesh everything out like so, even if you'll only use a tenth or less in your book.
----- Example
It's against societal norms for an 18 y/o to marry a 14 y/o today. In medieval times (true medieval), it's the norm, especially for political marriage. The couple may not see each other for a year or so depending on the parents' personalities and the personality of the couple, but ye, the marriage contract can be signed w/o going against societal norms.
This leads to concerns in a growing teen in those times that are not present in most countries of today (idk every country's situation, so most it is). Concerns such as being used as a political tool, being married off as a punishment for not behaving (depending on parents' personalities), stress and anxiety stemming from having to marry someone when they already have someone they love, etc. (ignoring status issues bc that's a whole 'nother problem).
Depending on the parents' personalities, "marriage" could very well be used as a tool to gain power or a punishment. Or the kid could have free reign.
----- Notes
Anyways, the point of all this. Let's specify that this is all limited to nobility, excluding commoners who try to rise in power through seduction and marriage.
That leads to the commoners, who observe everything through the rumors and gossips of their friends (the maids, house servants, butlers, chefs, etc.) having free drama delivered to their doorstep. This drama could then be sold for profit in the form of newspaper and gossip tabloids.
And the clincher, a witty noble character could use the commoner's newspaper to determine the situation of other noble households.
Voila. You got worldbuilding, free info network, an amazing and fleshed out chance to show the wittiness of a character, and maybe some depth into personalities of side chars if you do it right. All from fleshing out the societal standards and deducing how it'd affect the persons of interest.
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So ye, flesh out as many things as you possibly can because it'll show in your writing. Your readers can tell how much you know, how much has actually been envisioned, and how much research has been done just from the small details and little hints.
For the pantser writers, this is especially important since you could use little bits you left here and there and wrap them up into a new arc or reasonable event.
Ex: A noble household finding out about the tabloid, firing a bunch of workers, then enemy households using this chance to plant spies or ruin their reputation.
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The next method to having a good foundation: rooting everything in logic, no matter how fantastical. Just because it's rooted in logic, doesn't mean it's constrained. Just do it properly and leave some open endings.
----- Example and Notes
In my book, I rooted the magic system into logic, to the point the birth of mana and the mana cycles were defined. Even the elements and possible combinations; I also drew up a magic circle template for reference.
Why? Bc I didn't feel like remembering 40+ different elements and their combinations so I just broke it down then rooted into logic so I could deduce something if I forgot it.
The basic elements are: Fire, earth, shadow, water, air, light, and neutral. Neutral is the same thing as Natural mana.
In the magic circle, the bois are organized like numbers in a clock, starting with fire at 12 o'clock then going clockwise in the order I stated them. The opposing elements are opposite of each other (so water is at 6 o'clock) w/ neutral being in the center. Every element has a line drawing to the other 6, except for those directly opposite as the neutral mana is in the center (pic attached).
now the combinations:
fire + earth = magma. Self explanatory. Fire and earth are right next to each other on the circle, so relatively low difficulty and no neutral mana needed to regulate it.
advanced fire = lightning. Fire is heat, heat is energy. Lightning is electricity and energy. (if you're confused, think fire-benders).
fire + fire + fire = plasma
light + water = funky disco ball magic bc the light refracts of the water.
shadow + water = illusions that are tied to an abyss form depending on actual understanding, so a deep dark cave at advanced, and an imitated abyss at expert.
Etc. Etc.
Since I yeeted everything w/ logic, I didn't have to decide on the order of the elements, just the rotation to put it in. Then to add some variables to control the power level besides just "how much mana is yeeted in there" I created the factor of "understanding."
So if one understands the element of fire pretty well, they'll use less mana when using fire spells and the power will also increase. The forms that they can control fire will also increase as well (so lightning and plasma).
Thus affinities were created...
So ye, after I finished entertaining that rabbit hole, I ended up with a solid outline of the power system, how every person uses it, the history of a continent, the history of mana, the mana cycle, the history of magic circles, and how my mc would interact w/ the power system.
All from yeeting the elements to logic. After that everything just fell into place w/ little to no effort.
How much you flesh it out depends on how much you use your brain (or other's brains). It's normal to create new details, and even entire realms, countries, or worlds just to make the transition flow well with what you have originally.
Just make sure it doesn't end up creating plot holes and such and is done way before you plan to introduce them w/ some hints here and there. Otherwise the readers will be able to tell that it's all just spontaneous to keep the story going.
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You'll be able to tell if your foundation is "good" if you throw it at someone else for logic checks. Then the brainstorming session occurs with other details being created to flesh it out, a mini debate over the logic of it and trying to find possible plot holes.
You'll know if it's an excellent foundation if you make something on a whim while keeping the foundation in mind a few months or even years after making the foundation. Then, after narrowing down the details of this whim, you yeet it into your world's logic, power system, society, etc. and it fits in perfectly.
So far, my boi is excellent. Made the system back in 2021or late 2020 and no logic holes as of yet despite adding some... things.
---You can go to next chap if you want, I'll explain the things below since it'll be mini sections each.---
-Spoilers for my book below in case anyone is reading it-
Thing 1: I wanted to add a cultivation country for memes, tropes being made fun of, and ye. but this is a world of mana... so I made the one of the boi's interpret "mana" as "qi."
Background info: Mana is just an energy that's controlled through language. The original method is using one's will, the language of the soul. As all methods derive from this, the power of their soul determines how much mana they can use.
Magic circles or Visionary magic (no magic circle casting) carries the language of the mind, a.k.a. imagination/vision. Chants should be obvious. Most peeps don't know this though and basically accidentally cultivate their soul when using mana/qi gathering techniques by controlling more mana than their soul can handle, thus tempering it just like how muscles are strengthened while working out.
One's understanding and knowledge of what they're trying to do also affects the efficiency rate and thus the power output.
So the boi that was isekaid was a xianxia nerd who interpreted mana as qi. Thus the cultivation begins and the mana behaves like qi bc the boi wants it to and has the understanding/knowledge to make it do so with noticeable effects.
Life continues for the boi who attempts soul strengthening techniques and such (suffers a lot). Anyways, the part that clicks is, drumroll please, the cultivation attack skill things that I'm blanking on the name. Martial arts but cultivation. Since mana operates how I stated before, they're essentially just a form of visionary magic.
Had to yeet some things around though to make sure it fit in smoothly... Gotta make sure there's enough people alive when the mc is summoned so I can actually do the memes. Kinda hard when everyone keeps yelling Courting Death every 0.1 seconds and brags about exterminating clans so I just made them breed like rabbits and other details (such as housing and land issues) shall be omitted.
Thing 2: Needed "divine power" to somehow be different from mana so I decided to make it belief-dependent, following typical religions and such. It'd also make rising gods value the numbers of believers bc that's their source of power.
The detailed form of divine power is just slightly altered but highly concentrated mana.
The part that fits in perfectly: Needed a way for the gods to not be able to interfere as they please while also having the divine realm be "special." So I yeeted the gods into soul form only (remember how magic works above? technically only a soul is needed to use it).
Thus created the bottleneck and danger of ascending to godhood: shedding the physical body and actually crossing into the divine realm + having/making a small amount of divine power as the entrance ticket (otherwise you'd just die; no body but only soul? basically death).
Since they're in a separate realm, the gods would have to cross realms to affect the world which would consume an immense amount of divine power (unless they specialize in space/dimension magic, hardly a few do though). So often times, it isn't worth the sacrifice to interfere when they can just use believers to do their biddings for much less of a cost.
Some of this stuff just fits so perfectly you'd think that's how it should've been or always was. Anyways, there's more things, but we're over 2k words so not in this chap. Ping me in discord if you're curious.