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

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

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

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

Why are most girls not open to the idea of anal sex?

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

“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—”

“Tart!”

What does it mean when a guy says he doesn't want to ruin the friendship? Is he rejecting me or is there another explanation? Why would a guy choose not to risk the friendship if he has feelings for me?

“Cute girls?”

“I’ll put the kettle on.”

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

Study Warns: Carbon Dioxide Removal Methods Could Trigger Ocean Oxygen Crisis - Indian Defence Review

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

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

“Perv.”

Why do I (45, male) feel like I'm crushing on a girl (19, female)?

“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?”

“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…”

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?”

Have you or anyone you know invested in cryptocurrencies before? If so, which one did you invest in and how much profit did you make?

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?”

“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?”

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

Doctors Say You Might Be Eating Way Too Much Salt — Here’s How To Tell - BuzzFeed

“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.”

“No way.”

Essentially, what you do is show the character:

Why are men so attracted to big breasts?

“I need to do laundry.”

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

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

Why can't the ISS take a picture of Earth and prove to the Flat Earth Society that Earth is not really flat?

Create a context between this character and other characters.

“It’s not looking at you.”

“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.”

Is the Donald Trump Bible any different from a regular Bible? Has Trump altered its contents?

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

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

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

Why do women stubbornly refuse to let men lead, even though they are attracted to the man, and the man both loves and desires them? Why do they get angry and blame the man when he gets fed up and walks away, when it's entirely their own fault?

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

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

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.

Stolen iPhones disabled by Apple's anti-theft tech after Los Angeles looting - TechSpot

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

“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.”

“You need some tea!”

Is it true that most women like alpha males?

Do that and you can ground your characters quite quickly.

“Claire, I—”

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

Why do humans sweat while stressed?

“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.”

“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.”

“Claire! Why are you still up?”

What has been your best sexual experience?

“Exactly.”

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

“But they’re cold!”

What makes someone feel "rich enough" in different societies?

“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.”

“Nary a cute boy in sight.”

“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.”

“Exactly.”

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

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

“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—”

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

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?”

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.

“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.

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