The biggest challenge for new filmmakers is creating a story. Most have the picture in their minds of a scene or scenes that they want to show. To get to "the good part(s)", they often contrive short segments to get to the fun parts at the expense of making the set up interesting, logical, or satisfying. I think it is a good first start, whether 16 or 60.
Since you're both starting out, there are some important basics. My advice is that film tells a story. It is NOT ABOUT the cool zombie makeup, clever blood/gut spatter, fooled-ya' twist ending, etc. Those are the spice for the movie, not the substance.
Rather than worrying immediately about characters, description, dialogue or script, write a one page version of your story. Getting the idea onto paper (or computer) is the first step. Let's say the following is the premise of your movie:
"When a young man becomes the unwitting target of a demon escaped from Hell, he endures unimaginable horrors on a made-for-Hell video channel. He desperately seeks escape and save his family before his soul is locked inside for eternity."
This is called a logline. There are two stories here--the objective (what we see) and the subjective (what we feel). We NEED to resolve the subjective so the audience feels the story comes to an end. So we need to decide on our ending--he succeeds or fails. A fatal flaw is many filmmakers think it's clever to leave the ending open. It's okay if you don't wrap up the objective story (that's what leads to the sequel). But the audience cares about the characters. Emotionally their holding their breath so you need to give them an ending--happy or not--so they can exhale.
I often teach/coach others to start with a six-stage model of the story which follows Hauge's model. It boils down all the other approaches into a simple structure. 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
At this point, I would break it up into the "6 Act Model". Put a header on six index cards or sheets of paper. I would go through and put the elements of my story under the headings. For example,
Act 1 - Set Up (introduce the characters and situation)
[Home]
Will argues with his brother and sister. "Wait till dad gets home."
[City]
Shaun steps out holding a cube. He's hit by a car driven by Will's father.
Shaun stands and kills him. He then takes his clothes, wallet and car.
Shaun decides on his target will be Will's family.
Act 2 - Introduce a New Situation and a Complication
Shaun appears at the door, states he's here to upgrade the service and ...
waits to be invited in. Now the evil starts.
Will and his brother and sister are now trapped once Shaun leaves.
But wait, what about little Jimmy? Maybe Dad can help?
Act 3 - Formulate a Plan of Action to Succeed (character throws self in headlong)
Sis and bro are killed off.
Shaun now menaces Will, putting him through trials.
If he could just remove the box from the TV maybe ...
Will sees the pizza guy to the door. Then his sister's boyfriend arrive. They meet nasty fates.
Act 4 - More Complications and Higher Stakes (usually a major setback)
Little bro Jimmy comes home with mom.
Shaun makes it a game. If Will does something evil, he'll spare Jimmy.
After all, what Shaun really wants is Will's soul.
Removing the box does nothing.
Will makes a wager with Shaun. If Will wins, Shaun restores all his family members.
If he loses, he'll submit to whatever Shaun wants. Shaun agrees.
Act 5 - Final Push to Succeed with it looking unlikely (suspenseful moment, climax)
Shaun creates an almost impossible scenario for Will to battle in.
It looks bad until Shaun makes a remark which inspires Will.
At the last moment, Will pulls off the win.
Act 6 - Resolution and the Ever After
Shaun pushes it aside but other demons come from Hell and reclaim an angry Shaun.
Everything is back to normal. Will is relieved that his bro and sis are alive again.
The pizza guy delivers the pizza. They look at him weirdly.
** Jimmy comes running in with the cube that he found on the front porch. Will sees it and ...
** Notice that the subjective (emotion) is resolved--relief. This ends that part of the story. Then, if you want you can add the twist.
Now you can go back and add details and think about dialogue. The structure of the film is in place. You don't have to be overly specific at this stage; it helps to set up the dynamics and flow. Once you nail the story structure, you can focus on the characters and dialogue. Acts 1 and 6 don't need to be as long as the others. Most of the character and situation development are in Acts 1 and 2. Acts 3 and 4 are where you have the action rollercoaster when things happen to and around the characters. We learn more about them as we see how they react. It's building to Act 5 which is the central moment of your movie. Here we see the lessons Will (and Shaun) have learned. In Act 6 there may be a final hurrah but it serves to bring finality to the threat/opportunity.
In a formatted script (say with CeltX), one page is roughly one minute of screen time. So if you devote two pages to Acts 1 and 6 and four pages to Acts 2-5, that's 20 pages or roughly 20 minute film. While not exact, 1 page is about 1.5 hours of shooting*, so that's 30 hours to shoot or about 3 days. Since most of this can be shot at two locations--one for the car scene and then the rest at the house the estimate should be fairly safe. The more locations and cast, the more planning and time it takes to shoot.
(*lights, shot set-up, sound, make-up, direction/blocking, etc.)
Normally as a scriptwriter you don't need to think about this. However, as a writer/director you need to think about the real world issues--budget, time, location, cast, and props/makeup. Since you're writing to shoot this yourself, you want to keep those elements in mind.
Just to emphasize, I'm not saying this is how your story should be written. I'm giving an
example of how you could apply the principles to create a structured story. And JHar's advice is excellent. If you're interested in writing and filmmaking, read scripts and books on writing to see how others approach telling their story. Every script goes through polishing before being shot. Again, my suggestions are meant to help you explore bringing out the best in your script when making it into a movie. Good luck!
