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

Create a context between this character and other characters.

“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—”

“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…”

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“Tart!”

“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.”

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?”

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“I’ll put the kettle on.”

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

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

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

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.

“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.”

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“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?”

“Claire, I—”

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

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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?”

“No way.”

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.

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

Do that and you can ground your characters quite quickly.

“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.”

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“Exactly.”

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

“Cute girls?”

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“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.”

“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?”

“It’s not looking at you.”

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

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

“Nary a cute boy in sight.”

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“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.”

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

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

Ive been pretending to be okay and acting as normal as possible, but Im actually completely heartbroken after a recent breakup. Its painful and really affecting me, to the point where I cant concentrate at work, Ive lost my appetite, I cant sleep, and It feels as if my whole world has been turned upside down. I loved him so much. He said so many cruel things to me and it made me realize he must not have loved me the way I loved him, or he wouldnt have said such horrible things. How do I handle the heartbreak and why cant I accept that he didnt love me and just forget about him?

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

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

Essentially, what you do is show the character:

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

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

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

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

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

“You need some tea!”

“Claire! Why are you still up?”

“But they’re cold!”

“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.”

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

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?”

“Exactly.”

“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.

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

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

“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—”

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

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

“Perv.”

“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.”

“I need to do laundry.”