You can't have a story without characters. They don't need to be human. They don't even need to be alive. But if the reader doesn't have someone to focus on you're going nowhere fast.
For all of us, the goal is to create characters that live, ones a reader can bring to mind and identify with. Most of us could picture what Harry Potter looked like long before we'd heard of Daniel Radcliffe. In Casablanca, without even seeing what happened in Paris, we know enough about Rick to guess why Elsa's arrival is having such an effect on him. Even though we've never seen it, we can all extrapolate how Darth Vader would deal with someone having a loud cell phone conversation in a restaurant
However, for every character that leaps off the page or the screen to be remembered forever there are a dozen who languish in obscurity. And for every one of that dozen, there's a couple dozen more who never even made the cut. They were so flat on the page they couldn't catch anyone's attention.
Characters will make or break your writing, which means they deserve attention. The mistake I see again and again, though, is writers who give their characters too much attention. Their characters never get off the page because they've been buried alive and crushed there.
Some rules-of-thumb and reasons I've pasted together over the years...
Don't describe characters in exacting physical detail. Your audience doesn't need to know someone's precise height, weight, cup size, skin tone, inseam, hair color, nail polish, and eye pigment. They don't need to be told the exact tie pattern he's wearing, where her skirt hits her thigh, if he likes boxers or briefs, if she likes thongs over bikinis, how many fillings either of them have, or precisely what they're having at the restaurant for lunch down to drinks, side dishes, and condiments.
You don't need any of that in your writing. Honest.
Long descriptions bring the reader to a grinding halt. The longer the description, the louder the squeal of brakes. You're performing, as some folks like to say, the infodump. The writer is throwing out a pile of information at a time the reader wants action and forward motion (which is—for the record—always). It's wonderful to know that, as Jane steps into the street, everyone notices her Prada bag, Yves St.Laurent jacket, eel-skin boots, wedding band with matching engagement ring, the St.Christopher's medallion she wears outside her midnight-blue silk blouse, her sapphire eyeliner, and her $300 hairstyle that's starting to sag, giving her one loose blonde strand that hangs loose over her face in a kind of sexy way as she puffs and swipes at it with her free hand.
You know what's far, far more interesting than all of that, though? Why is Jane stepping into the street? Is it a crosswalk? Is she avoiding someone? Getting into a limo? Throwing herself in front of a bus? She's been frozen there in mid-movement while the writer (in this case, me) prattles on about her clothes and hair. Heck, by the time I got back to her you'd probably forgotten she was even outside.
There's another reason to not spend time on physical descriptions, whether you're writing a novel or a screenplay. Silly as it sounds, you don't have much say in what this character looks like. When people read, they form their own mental images, and they're usually pretty different from the ones that were written out. In Dan Abnett's Ravenor books, I always see the character of Kara Swole looking like my friend Penny from college. Their descriptions don't match up at all (well, they're both female gymnasts, but that's about it) yet this is how I picture Kara. For that matter, in the same books, I always see Harlon Nayl as Jett from Cowboy Bebop. As you refer back to your extensive description, you'll jar the readers out of the flow of the story as they think What? Blonde? I thought Jane had black hair? Jar them one too many times and they'll start to get resentful, and then they'll start to read something else.
If you're writing a screenplay, this is even more telling. It's really cool that you've described Lynne as 6'3" with raven hair, blue eyes, alabaster skin, the physique of a pro bodybuilder, and half a page of further description. Then Jessica Alba expressed interest in the part and suddenly Lynne was a 5'6" tanned brunette with a body built along very different lines. So you just wasted half a page and messed up the timing of your script for nothing.
So... extensive, elaborate physical descriptions are a no-no. Use broad strokes and fill in details only where you need to. Pick three or four good descriptive words for the character (not their clothes), and stick with them. Their dialogue and actions will bring them to life and your readers will fill in the rest.
In the novel I'm working on right now, for example, the antagonist I've just introduced is a pale man who's bald with tattoos on his head. There's hundreds of ways to interpret that description, but you've got a solid image in your head just off that, yes? Which means I'm now free to go talk about what he's doing with that AK-47, the ultimatum he's issuing for his boss... and he's already a bit more interesting and solid than Jane up above, yes? In about half the space.
Now, as far as the mental/ historical side, if this stuff is important, of course it should be included. If our main man has lost everyone he's ever cared about, if our heroine suffered from asthma as a child, or if an encyclopedic knowledge of rural New England history will be critical to resolving this mystery, then these things need to be in your writing. Again,though—no infodumps. If you introduce me to Robin and then explain how her hometown got its name, the name of her first pet, who she took to the prom, the state her parents grew up in, how she did on that second grade spelling test, and why she loves pink... there'd best be a damn good reason for all of that being in the first two pages, and it better all be important in the next 298.
That's the best rule of thumb for all of this descriptive stuff. Is it critical to what's going on within these pages? Your audience is going to assume if you're giving all this information, it's because they need this information. After the fourth or fifth exhaustive description of a character's jewelry, lunch time eating habits, or genealogy, your reader is going to make the assumption none of this is going anywhere and start skimming. First paragraphs, then pages, and then over the television listings to see what else could be filling this time...
Now, you can make an argument that any event in someone's past affects their present and every single decision shapes a person's life to some degree. Thus, anything you choose to include is relevant to the story on some level, yes? Again, though—this is not real life (please look back a few posts to resolve any confusion). No one wants to read about a character's personal history that does not have a direct bearing on what they're experiencing right now.
Again, for example...
I hate ketchup (and catsup). Honest and for true. Cannot stand it. Loathe it. Not for any flavor or texture issues, but for color. When I was five I was eating French fries and saw my dog, Flip, hit by a car outside the dining room window. Happened more or less right in front of me on Rt 1A in Cape Neddick, Maine. I could show you the spot today. I still remember his scream. And my screams. My mom and my little brother freaking out. And I remember the blood. And I've never been able to deal with ketchup since.
A formative event that still affects me to this day? Absolutely. I'd never deny it. Does it have anything whatsoever to do with the hints and suggestions I post here?
Nope. Not in the slightest.
It has nothing to do with my writing here, for CS Publications, or my own fiction, which is why most people reading this have never heard of it before. It has no business being in any of this. In fact, unless someone's writing a story where I've been replaced by an undercover agent/ alien shape-shifter/ android double and my girlfriend catches said doppelganger when he puts ketchup on his scrambled eggs-- this is a completely pointless bit of information about me.
Oh, but it builds character, you say? Expands the vast tapestry of my life? Tells everyone a little bit about me in so many ways? Makes me more human?
(Feel free to read that out loud in a Stewie Griffin voice)
You've got an actual story, don't you? If you want to focus on one thread in the tapestry of my life, choose one that shows the reader how my life relates to that story. Don't waste their time with something that has no bearing on the book/ screenplay/ short story they're reading.
Let the audience know how annoyed I was at thirteen when a doctor told me during a physical that writing wasn't "a real job." Explain how thrilled freshman-college-me was when he got a personal letter from Tom DeFalco rejecting my Marvel pitch but with hints and tips about how to improve and try again, plus a full copy of one of his Thor scripts for reference. Give them the visual of me in a panicky, cold sweat sitting outside Ron Moore's office, waiting to pitch a few Deep Space Nine stories I'd come up with that had impressed a long string of script readers and story editors.
See? That's all relevant. You're reading and saying "Wow, this guy's been serious about writing for a while now, hasn't he?" That's the kind of stuff that should come out in your writing.
And you've already forgotten my dog's name, haven't you? And the name of the road he was hit on? No worries. He'll always be important to me, but I understand why he's not important—or relevant—to you. Honest, I do.
Now, go write.