When writing a novel, how can a character be developed well, but QUICKLY?

“Claire, I—”

Essentially, what you do is show the character:

“Well, maybe if you didn’t spend all day reading—” May prodded the book with its garishly-coloured cover with her foot. “Bizarre comic book porn…”

All international travelers should get measles vaccinations, CDC says - AP News

“I’m serious!” Claire said. “It’s staring straight at me.” She let the curtain fall. “Weird.”

After Eunice and I finished London Under Veil, I entered the first chapter in a contest at a convention where you could submit something and have it critiqued by a professional book agent.

Claire, one of May’s three flatmates, former university roommate, and best friend in all the world, shrugged expansively. “It’s a Saturday night. What else would I be doing?”

Broadcom Stock Falls Despite Earnings Beat From AI Chip Maker - Barron's

“Thanks. You’re looking pretty ratty yourself. Have you been in that bathrobe all day?”

“Well, maybe if you’d wear more clothes, they wouldn’t feel so cold. Hussy!”

May studied the black and white comic panels. “Oh, my. She looks…anatomically implausible. What is she doing to that poor man? Wait, are those cat ears?”

What is the reason behind some people wearing trunks instead of speedos when swimming in pools?

“Claire! Why are you still up?”

“Damn straight. So get to it! This time next week, I want to hear some moans coming through that wall.”

“Exactly.”

A child had measles at Mall of America, concerning state health officials who don’t know source - Star Tribune

“Why is that always your first suggestion? I do not need some tea. It’s three o’clock in the morning! If I have tea, I’ll never get to sleep.”

“It’s not looking at you.”

“But they’re cold!”

Why are Trump supporters so incredibly stupid?

Claire sat back down, legs tucked elegantly beneath her. “You are looking a bit sloppy,” she said, inspecting May through narrowed eyes.

Doing something they enjoy, that expresses their personality, and that is in some way unusual or noteworthy;

“I’ll put the kettle on.”

What blowjob techniques do you use for your man to cum inside your mouth?

“Yuuna and the Haunted Hot Springs!” Claire turned the book around.

“I need to do laundry.”

May yelped. “Hey! Your feet are cold!”

Why is there so much hate against black people?

“So you didn’t meet any cute boys at the club tonight?” Claire called as she bustled about the small kitchen.

Here’s how we presented the character Claire when she was introduced, which the agent particularly singled out:

May pushed Claire’s feet away. Claire rose to peer out the window. “Huh. It’s still there.”

Graphene Is Stretchable? Physicists Make “Miracle Material” Bend Like Never Before - SciTechDaily

“I’m glad my sex life is so entertaining.”

“About wearing more clothes? How am I supposed to catch any fish if I don’t show off the bait?”

They both burst out laughing. “I’m right, though,” Claire went on.

Why does it itch on my vulva, uterus, and sides of my vagina, but it doesn't itch inside the vagina?

In the kitchen, Claire set out a battered pair of mugs: May’s black, with “PEBKAC: Problem Exists Between Keyboard and Chair” in white letters; Claire’s white, with “This must be Thursday. I never could get the hang of Thursdays” in dark blue. She carried both mugs into the living room. “A moggie followed you home? Is this some weird Internet slang I’m not current on?”

“You need some tea!”

“No, about the cat. You don’t need a cat. You remember what happened to your spider plant, right?”

Do you have any opinion on Japanese writer/actor Yukio Mishima?

“None of those either. Look upon the wasteland that is my sex life, and see that it is barren. Naught but a moggie followed me home.”

“Hang on, are they playing ping-pong?”

“Yes way. It’s washing itself under the street light. Uh-oh, I think it spotted me. It knows I’m watching it. I swear it’s looking at me.”

“They are! He broke the rules of the boarding house by petting this character while she was in cat form, so they invoke the ancient rules of single combat via ping-pong, and—”

“From the look of you, if you try to sleep now, you’ll spend the next three hours hanging onto your bed trying to stop the world spinning. Since you’re not going to sleep anyway, you might as well keep me company.”

“You know what? Never mind,” May said. “I am way, way too drunk to be having this conversation.”

Do that and you can ground your characters quite quickly.

“Nope, I mean a cat followed me home. A black cat, to be exact. All the way from the club. Probably still out there, for all I know.”

“Cute girls?”

“Number one, it’s not porn, it’s ecchi, and number two, why would I waste a perfectly good Saturday doing anything else?” Claire pulled at her tea and sighed. “The only thing that could make this day better is if you'd come home with some cute boy, so that after you kicked him out tomorrow I could live vicariously through you.”

“I don’t know. Partying. Going to a pub. Anything besides sitting on the couch reading…” She squinted. “What the hell are you reading?”

The agent had only one bad thing to say (the synopsis was crap; writing synopses is hard!), but praised the characterization and particularly how well we introduced a character’s personality quickly.

“Tart!”

“Nary a cute boy in sight.”

“Perv.”

“I try not to, but thank you for reminding me. I know I don’t need a cat. I don’t want a cat. What would I do with a cat?”

“No way.”

“May! You’re home late! Early, I mean. Well, I mean, it’s early in the morning, but you’re home before I expected. Er, after. Before?”

Create a context between this character and other characters.

“I know! That’s why I’m putting them under you!”

“Yep!” Claire chirped. “There’s this schoolboy, see, and he’s homeless, so he lives in this boarding house that used to be a hot springs bathhouse, which is cheap because it’s haunted, so he decides—”

Engaging in conversation that also shows something about their intelligence, personality, wit (or lack thereof); and

“I’m just a fan of your catch and release program.”

“You don’t need a cat. You can’t take care of a cat. You can’t take care of a ficus.” Claire flopped on the other side of the sofa and wriggled her feet beneath May.

“Exactly.”

“Fine.” May collapsed into the warm spot Claire had just vacated.

“It’s a cat. All cats are weird.” May sipped from her mug, inhaling the warmth. She closed her eyes. The room spun. She opened them again. “Ugh. I think I drank too much.”