At this point you've probably heard or noticed, that all characters a writer makes carry a bit of that writer with them. Their personality, their voice, culture and bits of their wishes.
This might come out in more or less obvious ways, from self inserts to all characters having the same voice and a plastered on personality. But it also heavily influenced the plot and the entirety of the world understanding.
Realising your own influence on the character, and making them independent from you will bring a lot more color to your gallery of personalities, and will hopefully help make some characters more than just enablers to make the protagonist shine.
How do you influence your characters?
Age and gender:
The most simple influence is your age and gender. These affect your life experience, level of empathy, maturity, patience, political views and so on. Plus, depending on your age, different things become important. A 14 year old girl is much less likely to be into a political drama, than a woman of 45, and has less life experience to see through people's feelings, because they haven't been in those spots themselves yet.
Gender is also, rather famously, an example. But on more layers than what papers usually bring out as manchouvanism.
Men and women have different fantasies and different writing styles. It's everything from women using more adjectives, to idealizing the opposite genders.
These two, are probably one of the biggest influences if you write romance stories. Extremely so.
This also means, that you write characters that are often similar in age to yourself when you start out writing.
Personality:
Quiet people that think before they talk will automatically make less reckless characters, and airheads will make more reckless characters. Your personality does come out in both characters and writing style. For example: I can't write an airhead without making them seem unreasonable and annoying. They're so far from my personality spectrum that it's hard to write them.
Your fantasies:
Which Clichés we use, and how we use them, is a strong influence we can have on the story, and it comes both from our age, maturity, personality and culture.
A typical example in manhwa, is the guy that goes into a dress store, and buys everything. Not everything she wants. Everything.
The girl acts all shocked like she doesn't want it. Acting frugal and poor, as she usually is.
And yet this happens and is treated as romantic.
Basically, the author thinks this is romantic. To be spoiled beyond belief and get everything they could ever wish for, even if they pretend to wish for the opposite.
Meaning, the girl is deceitful too. The character might say she's not there for the money, but the plot and the situations are saying the opposite.
If you don't believe me, let's take it out of context it's born in.
A girl marries one of the richest men in the country. He's an asshole to everyone. Famously so. They both consider it romantic to go into Gucci store or whatever else is the most expensive clothing store in the country, and he buys all the clothing in the store.
I would have been horrified by the immense waste of money of the guy just choosing everything without any regard of whether it suits me or either of us like it. He basically doesn't care about it and is just throwing money at it to make choosing someone else's problem. And she thinks it's romantic.
This doesn't necessarily mean that the writer that wrote it is materialistic, but there is a little dream in there that calls: "I want to be spoiled, and never again lack anything" and that wish manifests in scenes like this.
I think part of it may originate from high number of housewives, that can't really spoil themselves with the money the husband earns, at least not without feeling guilty, so they hope to be spoiled. This is of course just an assumption, but it's an exercise in understanding others choices and point of view, and see how our own hopes affect the stories we make.
Your life situation:
As much as I am not a fan of the lazy main character, that has no energy for anything and just dallies about, the character type is there for a reason, and you actually do see it in the beginnings of those stories.
They are burned out.
Life is hard, and when you hit that low, imagining being happy can seem distant and vague. The closest thing, is dreaming of relaxing and recharging energy.
I often find that characters like this, however, never stop wanting to relax. They, like the author, often don't actually regain the energy you'd expect of a normal refreshed person.
As authors we can very easily put our own energy level into our characters, and it can affect both plot and feel of the story.
If we can't fight our everyday, then sometimes we lower the difficulty of our characters as well.
This also means, that if you're a mother, then you're more likely to write a story from the perspective of a parent.
Culture:
If you only read or write your own culture's stories, then you probably won't notice as much, but there can be massive culture shocks in stories as well. Of course, something as simple as 'no rise' can be a big thing to some, but I find that the parts about family, create a bigger contrast, because they can be understood so differently.
Take for example a young kid. Make them do a curse word at their mother. The mother than smacks her kid with a sandal.
Now, in some cultures this is expected. The kid did something respectless, and was punished. In others, this is child abuse that will get protective services called and the kid moved to a foster home.
Now imagine people reading your story, with a scenario like this in it. The situation will be received wildly different, depending on the reader, despite you thinking of it in one specific way.
Being aware that this can happen, will help you set a situation up a bit more clearly as well, so you can adjust the scene to make it make sense for everyone reading your story.
Your writing and speaking style:
Yes, this too.
Are you, like me, prone to using long sentences? Maybe a hint of purple prose?
Both your writing style, and the way that you yourself speak, ends up having an effect on the voice of your characters. If you're prone to using metaphores and simili, then often, your character will too.
If you're used to using slang, then your characters often will too, unless you make a concious effort to avoid it.
This can also mean a very elegant(supposedly) character ends up cursing like a sailor, or sounding like a street kid, instead of what was envisioned, or opposite, that a very simple and blunt character ends up making very long and complicated sentences that doesn't suit their characters.
Stereotyping
The very first step in gaining control over your own influences, is probably by using stereotypes.
I used to do written roleplay on Gaia online when I was younger, and I specifically had two close friends I wrote with. However, both of them had the same tendency. No matter how many characters they made, they all had the same personality, just with a new backstory and body. I don't think either of them was aware of it, but imagine the same situation for a full story, where all characters are similar, or if every story you make is basically the same character, but with a new plot pasted on.
Of course I deal with this problem too. I'm usually very calm and thinks things through, so young kids and airheads are extremely difficult without making them look like idiots.
Basically, my personality is more suited for intrigue than a teenage love drama. In the end, ridding all of your personality from the characters isn't possible, but you can mitigate a good deal of it by making a conscious clear cut line between you and the character.
I find that I personally do this the best by starting from a stereotype.
Yes, a stereotype.
I know.
But hear me out.
Stereotypes, or types of people we have seen before and categorized, are very clear cut. We can approximate the way they'd feel and react to certain events, even if we might not agree with them. But as I said, that's the starting line. Many people don't move past here, but this is the point where you have to take the stereotype seriously and flesh it out, to go to the next step, and thus also adjusting it to the setting.
"He's a person boundlessly good and generous to the person he loves." Why? Why does he buy her an entire store worth of clothes on what appears to be a whim to make her happy?
No person is that boundlessly good. Partly because humanity isn't that perfect, and also because buying a store worth of clothes to make your girl happy, though she told you not to buy everything in the store is... Dumb.
This is what I assume is the real reason: He saw a successful store. Decided he could earn a good profit by buying it, bought it, then didn't tell his girl and then 'bought' everything in there to look good for her, while putting in as little effort in actually chosing something for her as possible.
And with just that he's already more fleshed out vastly more than he was a minute ago. He's putting up a facade towards her and no one knows how much is sincere.
You might say I got a rather negative answer out of that, but when you have that much money, then it's not how much you get, but what you get that matters, and why. Throwing money at the problem, and hope there's something she likes, is the laziest and least caring option I can think of.
Then again, this too shows my own influence, culturally, and maybe that economically I am well enough off to see the situation like that.
The exercise of picking things apart
I do think it's a good, but at times sad exercise to try to pick things apart like this, also because you can avoid falling into using these clichés without thinking about why they're there, but also to improve your understanding of people around you.
Just picking apart the reborn as a villainess genre can tell you things about the culture and life situation the writer comes from, or what they think of the culture around them.
The more detail you can go, depends on your own empathy skill. How good you are at understanding people's point of view.
Of course it's possible to overanalyze things, as it always is, so trying to see the possitive sides of things, is important too.
He might have chosen the laziest way to give her some new dresses, but she was happy, so he did exactly what she was hoping for, and thus he made the right choice.
Tldr: Basically, start out with the stereotype to create the basic voices, and then pick them apart and consider why, to give them their little secrets. That's how I make their voices just that little bit more unique.