Okay, time to share the "secret weapon" again.
(bear with me, OP, you will *never* forget this)
When I started out, my MC was reading "okay", but I myself complained about the side characters.
I heard a reviewer call some movie "cardboard cutouts" for characters, and I realized THAT was what I had.
My HERO I "knew who they were" as authors say in their own secret language,
what "the Oracle" (my pet name for her)
@Eldoria defines in her Advanced Calculus textbooks as "characterization"
I was particularly vexed by the inability to do "banter".
Certain things are compulsory for genre, and the two uniformed middle age beat cops bantering on scene to the murder,
waiting for the detective to arrive? I wanted them BS-ing. I couldn't even do that credibly.
What do? Ask anyone I met, and complain. Sooner or later, someone will say something useful.
(there was no Oracle for me back then, lol)
I was talking about my shortcoming complaint with a used book store owner I was friends with.
Said owner walked over, picked up a used paperback, and handed it to me.
"What's this."
"Its a book. You read books, you learn things that way."
"Smart ass..."
"Seriously. You might hate the book? But you need to read it."
"Why?"
"Remember you read Airframe by Crichton? And you were talking about how to build an airplane was interesting?"
"Yeah. So."
"You read this? Your characters and dialogue will instantly get better."
The book had a unique plot.
Female MC, a female entertainment lawyer. She specialized in authors and in particular... nom-de-plume authors.
The lawyer represented the author in all negotiations, no one got to ever meet the new author.
As a hobby author over the years, the lawyer herself had finally shit out solid gold for a book.
Two then three publishing houses were interested.
Movie rights were being discussed and a sort of a small "bidding war" had erupted.
Two publishers were slowly rising their advance offers to land the publishing deal.
A Hollywood assistant to a producer was at lunch when one discussion went down over lunch...
movie rights were getting an offer thrown out, which made a rival producer take notice and try to outbid the rival.
Big success was right around the corner!
The big secret was... the lawyer herself had written the book, but it was an action novel.
Male author was a pen name. No one knew.
She decided to hire an unpublished author who she thought "looked/acted" like the "author".
(He had been in the service, had been a real life tough guy when young)
He had his OWN book he had written, and she read it to see.
I remember it was a "Tom Clancy international thriller clone", described as "adequate" for the genre.
Her and him, were discussing writing. He asked her for pointers, because her book was blowing up, how had she done this.
The ONE bit of advice she gave him, which I NEVER forgot?
(the rest was generic, you heard it all before)
"I use character models."
Then she explained...
Why create a "bio sheet" and write a short story of the "backstory" of each character.
Use a REAL LIVE PERSON for the "character" and model the character on THEM.
(her hero was based on her little brother or something)
Now, she knew what her character would say. How he would say it.
She knew how he stood, how he walked. What he would stop to look and marvel at.
She could describe everything about him? In startling detail.
She even knew how he "thinks", because little brother grew up with him, understood his thought process.
She said you always use a REAL PERSON for the character model, now you;re writing a "real" person, so its now easy.
Easy to make them "come alive".
They have flaws and foibles, shortcomings. The hero now has little fears and things they are uncertain about.
You just NEVER tell anyone, who the real life character model was.
Could it really be this simple?
I was doing "writing exercises" to develop "two beat cops bantering" before the detective arrived on the murder scene.
Wasn't working, at all.
Might as well try it, I suppose.
I imagined the two beat cops? As these two older guys at the truck stop I was a regular for years as one of the coffee crowd there.
Holy shit. All of a sudden? The "two beat cops" talking about their health and home life complaints? was very "real".
I could describe their mannerisms, describe them, everything.
I could just "see" them doing it !
Big test. Always wanted a secretary on this one story.
I picked out... this one truck stop waitress.
I simply took HER, and put her in "secretary clothes" and kept everything else about her.
her looks, her way of talking. Her personality. How she dressed outside of being a waitress.
her vehicle she drove. Her stories about her love life... everything.
her attitude and "way", her gestures.
she was that one waitress that gave you "sass" but everyone enjoyed it.
Another instant success. My minor character now had everything... real.
IN SUMMATION:
why try to use the "bio sheet" to create a "real person" out of thin air.
(Its harder than you think)
why use the "overlapping circles" of "personality" to create a real-seeming personality?
JUST USE A REAL LIVE PERSON!
I mean, its what you want in the end? A real person to write about?
So just START with one!
Now? you can describe them. You know how they walk, talk, pop gum and annoy you... everything.
you can just close your eyes, and "hear" them saying something.
Works perfect for odd-couple "buddy plots".
Works for small groups. Works for side characters, bit parts, everything.
PRO TIP:
you might want ONE "model" for looks, and another for everything else for the same character.
You see, we all hear the same advice.
(Easier said than done)
"Know your characters, inside and out"
"Your characters should seem very real to you"
"Create flaws, real people have real flaws"
"You should stop and say... but my character wouldn't DO that, they would do THIS, instead !!"
Enjoy.
NOTE: this fixes everything about characters.
Credible dialogue. Voicing. Grammar and speech patterns. Flaws, misconceptions, unique personality.
You're welcome, OP.