Three-act structure? Character arcs? Forget all that Syd Field nonsense and start cranking out scripts using James' 10-step movie making method.
STEP 1: FIGURE OUT YOUR WITTY SLOGAN
For example, see if Sean Penn is taking a break from one of his lefty causes and available to act, and imagine the movie trailer guy: "This summer, the Penn *is* mightier than the sword." The film practically writes itself from there. Voiceover guy can be great inspiration for movie concepts. Or you can just picture Tyler Perry dressing up as a black woman. Again.
As an aside: Men in Black director Barry Sonnenfeld practically had an aneurysm when he found two leading men with the anonymous names Smith and Jones.
STEP 2: ADDING THE 3D
This is very important, since popcorn has now surpassed the price of oil at most multiplexes, and this is the only way that theaters can get all your spare change without installing metal detectors.
After you create your awesome movie concept from the witty slogan (e.g. "This holiday season, Santa joins the police force"... cut to elf with a .45 in someone's face screaming something about being a bad boy this year), you MUST consider the 3D.
The best way to handle this is to add explosions, unnecessary car chases and flying sequences. Think about a levitation machine in a ball-bearing factory ("This fall, it's going downhill", etc.)
STEP 3: GET THE POSTER DOWN
Whether you have Photoshop or a pub napkin, story development doesn't start until you have a poster. I would recommend combining two existing posters for plot ideas.
For example, Anne Hathaway is one of the reasons I can't sleep at night since I'm scared she might try to eat me. Anne Hathaway in a clown suit is the most terrifying thing since Kim Kardashian got a TV show. Basically, it's The Princess Diaries meets Steven King's IT - see, I crapped out that idea faster than they made The Tourist.
STEP 4: IS YOUR HERO INTERCHANGEABLE?
One of biggest problems with most story ideas is that they are character-driven. People learn this from reading the classics at school, but actually all successful films now are plot-driven.
Can your middle-age taxidermist be replaced by Hannah Montana? If not, you've tied your plot to the character - so fix it! This is important since when a star reads your script, they'll immediately change all the main characters. And probably the entire plot too.
This technique is also useful for generating plot ideas. For example, tired hack Helen Fielding managed to squeeze Bridget Jones out of Pride & Prejudice just by flipping around a few details (see step 10 for more about stealing from the dead).
STEP 5: ADD THE EXPOSITION
Explosions, car chases and gratuitous CGI have a tendency of getting in the way of pushing the plot down the plank. Although shunned in decades past, this is where voice-over and redundant characters can really help throw audiences a bone like the ravenous dogs that they are.
Different studios have different approaches here. For example, Disney films voice-over the first 5 minutes to make sure the A.D.D. generation has a chance to understand what's happening while playing Angry Birds. Christopher Nolan uses second-rate performers like Katie Holmes and Ellen page to read the story to us. And Michael Bay just doesn't bother with a plot at all.
STEP 6: ADD THE MERCHANDISE
Take a lesson from the masters here: Steven Spielberg and George Lucas are responsible for more retail plastic crap than if Bed, Bath & Beyond and Cost Plus mated and had an overweight supercenter child. We're talking dolls, we're talking posters, toys, calendars, key-chains and more junk spewing out than if Cafe Press and Zazzle's inventory computers both got a virus.
This is also a very good way of adding depth to your characters without any real work. Think about Jurassic Park - Dr Grant and Dr Malcolm are two of the worst scientists since dinosaurs actually did walk the earth. They're probably responsible for Intelligent Design education because their science sucks so hard it can create a vacuum in a wind tunnel but.... wait, holy shit, check out those dinosaurs!
See? And who didn't own a build-it-yourself T-Rex with adjustable half-eaten lawyer?
STEP 7: GET ONTO THE SEQUEL
Uber-writers Ted Elliott and Terry Rossio will be the first to tell you this after Jerry Bruckheimer went all Frankenstein on their Pirates of the Carribbean script. They made the mistake of having one excellent self-contained little story, leaving little room for second, third and fourth outings when Bruckheimer started threatening to remake Thundercats if they didn't get their shit together. Ted and Terry started scraping the barrel in #2, went almost through the floor by #3, and for #4 they've had to lower their standards so far that Penelope Cruz is now involved.
To save yourself from this fate, you should immediately imagine your second film with the lead replaced by Shia LaBeouf. Where's the beef? Shia LaBeuof.
STEP 8: WORK OUT SOME BACKUP GENRES
Although I'm incapable of seeing Anne Hathaway in a clown suit as anything but horror, more talented writers would be able to pitch 3-4 films with the same concept as comedy, romance, science fiction or TV movie. In the case of The Mummy 4, they did all five at once.
This is also a good place for story generation - just imagine The Hangover as a science fiction, or Insidious as a horror instead of an unintentional comedy.
STEP 9: ADD MORE PLOT TWISTS
A recurring problem for newbie writers is not making your plot convoluted enough, yet it's an easy device for masquerading a steaming turd. Look at The Bounty Hunter, a true cinematic abortion - had Jennifer Aniston killed herself in Act 2, I wouldn't have left the theater crying. Or how about Splice, which unexpectedly added some part-mutant sexual weirdness at the end to make you forget there was no plot beforehand?
When you've finished telling your story to yourself, ask "And then?". And then ask "And then?". Before long, nobody will have a clue what's going on but it'll look really cool and you'll be sat on a beach sipping margaritas.
STEP 10: DON'T BE AFRAID TO RIP OFF A CLASSIC
As mentioned in my Tangled review, Disney is the king of dead writer desecration. While screenwriting can be fun, there's nothing more fun than jumping up and down on the graves of famous storytellers and using their legacy like a bouncy castle. As it says on the walls of the Disney executive boardroom: "Dead people can't sue" (it's right next to the death warrant for the makers of Mars Needs Moms).
Where did the writers of Ghosts of Girlfriends Past turn when they discovered they had no writing talent, creativity or purpose in life and when even the organ donation people turned them down? Charles Dickens of course. Now in reality, Dickens is so white and powdery in his urn that Charlie Sheen's already snorted most of what's left, but his work is OOC. What's OOC? Out of copyright. That means any asshole - such as Jon Lucas and Scott Moore - can trample the works of one of the world's greatest writers. It's like throwing a can of paint over the Mona Lisa - it's just so much fun.