What sometimes helps is to start by writing a treatment of your idea. It's basically the script's plot without dialog. At this point, as Geckopelli said, don't labor over one scene. Get the story idea written down. Don't worry about all the detail that creative writing teachers say are needed. That's true for books and short stories, not screenplays. HOWEVER, plot and character development ARE IMPORTANT. While some writers let their stories evolve as they write, my work with students is that new writers are still struggling with their stories. At least in the beginning, planning makes the process easier.
I don't believe in "formula writing". However, in working with others, I have found that outlining action helps guide script development when starting out. Everyone here has different techniques which work for them. Some use index cards, others just start writing. My advice is that film tells a story. So rather than worrying immediately about characters and description, write a one page version of your story. Getting the idea onto paper (or computer) is the first step.
"A boy sees a girl across the street, and he falls instantly in love. He goes to cross the street but the lights are against him. He sees her get on the bus and his heart falls. He grabs a pen and writes the bus number and time of day on this palm. He goes back the next day a half hour early to see if she is there again. She doesn't show. He's disappointed. The bus pulls up and leaves. Just then the girl comes running up and is upset because she was running late. ...."
At this point, I'm not sure how I want it to end. I haven't really thought about the boy or girl. But I've started my story going. At this point, I would break it up into the "6 Act Model". Put a header on six index cards or sheets of paper. What I'm going to talk about can be found at Michael Hauge's site:
http://www.screenplaymastery.com/structure.htm
Act 1 - Set Up (introduce the characters and situation)
Act 2 - Introduce a New Situation and a Complication
Act 3 - Formulate a Plan of Action to Succeed (character throws self in headlong)
Act 4 - More Complications and Higher Stakes (usually a major setback)
Act 5 - Final Push to Succeed with it looking unlikely (suspenseful moment, climax)
Act 6 - Resolution and the Ever After
I would go through and put the elements of my story above onto the index cards under the headings
Act 1 - Set Up (introduce the characters and situation)
A boy sees a girl across the street, and he falls instantly in love.
Act 2 - Introduce a New Situation and a Complication
He goes to cross the street but the lights are against him. He sees her get on the bus and his heart falls.
Act 3 - Formulate a Plan of Action to Succeed (character throws self in headlong)
He grabs a pen and writes the bus number and time of day on this palm. He goes back the next day a half hour early to see if she is there again.
Act 4 - More Complications and Higher Stakes (usually a major setback)
She doesn't show. He's disappointed. The bus pulls up and leaves.
Act 5 - Final Push to Succeed with it looking unlikely (suspenseful moment, climax)
Just then the girl comes running up and is upset because she was running late.
Act 6 - Resolution and the Ever After
??? Maybe, I'll have him small talk with her. They hit it off and go grab a cup of coffee.
Now I can go back and add details and think about dialogue. The structure of the film is in place. I want it to be a bit more robust so,
Act 1 - Set Up (introduce the characters and situation)
A boy sees a girl across the street, and he falls instantly in love.
- The boy is dressed in a giant Hotdog suit advertising for the deli behind him.
- The girl sees the giant hotdog and flashes one of those "you're adorable" smiles.
etc.
A treatment version of this story might be:
"Doug lopes out of Mr. Willard's Hotdog Emporium dressed in a giant hotdog costume. He passes out fliers to pedestrians who sidestep him or stare. As he glances across the street, he sees an attractive girl. She gives a coy smile and turns. He glances about and decides to advertise on the other side of the street. The suit makes it difficult for him to cross with the crowd at the crosswalk. Doug sees her get on the bus. As she sits down, she looks out the window at him. He desperately grabs a pen and writes her bus number down on his palm along with the time.
Doug is in his apartment fussing with his hair. Doug comes back to the bus stop a half an hour earlier and waits for her. He keeps watching the clock impatiently and heaves a sigh as the bus pulls up. The driver asks him if he's getting on. Doug says no and the driver slams the door closed. Doug sinks and starts towards the crosswalk. Suddenly the girl appears running up shouting as the bus pulls off. Doug turns as she screams and scowls. He looks over at her and waves. She sees him and turns. He skulks into the Hotdog Emporium. He's seated at the counter when she enters and asks for a chili supreme. When she turns she heads towards him and sits a short distance away and starts talking on her cellphone. Doug builds up his nerve to approach her. At first she is tentative but when he sits down she is relaxed. Through the window, the two are seen smiling and laughing. Another employee is in the hotdog suit outside of the window."
Now you can go back and translate that into a script by adding scene locations (slug lines), description, dialogue, and actions.
Code:
EXT. BUSY CITY STREET - DAY
The skyline looms as the feet of pedestrians scurry along.
Out steps leotards with basketball sneakers.
A large hotdog steps from the doorway of the "Hotdog Emporium".
From a hole in the center, DOUG's face emerges. Doug is 18 and
scowls as he drags himself in front of the window and waves a
sign.
As he smiles and tries to hand out fliers, people walk around to
avoid him, break out laughing with their friends or scurry past.
A young kid looks up at him and sticks out his tongue.
Doug's eyes squint, he wrinkles his face, and sticks his tongue
out.
The mother shoots Doug an indignant look and pulls her son along.
Doug heaves a sigh and glances over at the bus stop.
AMANDA, an attractive 18 y.o., waits for the bus dressed in an
apron. She watches for the bus when she notices him. She
shoots him a smile.
Doug looks at her and smiles.
He glances back then looks over at the empty corner across the
street near the bus shelter.
A beat. He makes his way towards the crosswalk light but ...
the pedestrians come like a horde as he fights his way there in
the awkward hotdog suit.
Amanda watches him with amusement. She turns back.
He's standing at the light as she gets on the bus. He watches as
she moves and sits by the window.
INT. BUS - DAY
Amanda looks out the window as it drives past. She sees him on
the corner waving to her. She moves her hand to lightly touch
the glass.
etc.
The action statements suggest the kind of shots one might see. The language is mostly active tense. Rather than say "he feels embarrassed", I try to show it via actions and responses. You want the reader/audience to get a sense of the character's personality. Let the actors do their job. The scene and costume description is minimal to what is needed for the story. Let the art director, set designer, and costumer do their jobs. The screenwriter needs to focus on story action and dialogue. So far there is no dialogue. That is the hardest feature of screenwriting. It is so easy to put in more words than needed to effectively convey a scene.
The Scriptwriter's Bible is a useful resource. However, the best way to learn any skill is to read successful scripts (and sometimes less than perfect scripts for comparison) and write. The trinity is Story, Structure, and Format. While structure and story are often intertwined, some stories do not make good movies. And some structures (linear vs. non-linear) work better with some stories. Starting with a structured approach in the beginning is often most instructive. As you become more experienced, you can try new ways.
Since you're adapting your story, try first re-writing it as a treatment, a barebones description of what happens in the story. It's bland by creative writing standards but provides a good starting point for developing actions. Don't worry about dialogue. This isn't a radio drama but a visual drama. Focus on the audience/viewer/reader sees. Once the visual pieces are in place, you can give your character's voices.
And a final word, scripts are blueprints. If sold or optioned, the director and/or actors will probably change what you've written to fit their visions and interpretations. That's just the nature of it. Don't be too wedded to your script. Do your best to present your story in the way that pleases you.
Good luck with your future writing.
