For me, a "tool" is some process, habit or approach that can be taught. When I teach screenwriters at USC's filmschool, I can't help the students with talent or luck, which are by far the two most important factors in a screenwriter's success, but I can give them tools. Likewise, I can't really teach imagination, stamina, or even self delusion (important as these three are). Practical knowledge of industry standards as well as willingness to listen to honest feedback, are certainly necessary, but I expect both of these when a student walks into the classroom or an aspiring screenwriter asks me for advice. What I try to teach is a process.
So, the most important tool in the screenwriters' toolkit is...
The Rewrite Cycle
Anyone who takes screenwriting seriously must commit to a continuous, circular process of collection, collation, execution, and presentation.
In later cycles of the rewrite loop, collection is the phase in which a writer patiently collects every note, suggestion or criticism he or she gets from people who have read the current draft. Some notes will seem helpful, some will seem unhelpful. Some will be exciting and others infuriating. The key is to collect them all patiently and without judgment. Write them all down. Treat every single note as a gift, one that will be unwrapped and examined sometime later.
In later cycles of the rewrite loop, collation is the phase in which the writer takes all the notes received from readers, collaborators and/or employers and sifts through them all. Too often beginning screenwriters either accept every note they get without question, or stubbornly refuse to take any at all. A veteran screenwriter does neither.
Instead, the veteran organizes notes according to character, structure, tone, and clarity. He or she looks for notes that come up repeatedly for every reader, and notes that some catch but most miss. Rather than reject suggestions that make the him bristle, the writer looks for deeper meaning behind the note. If the readers aren't getting what was intended, does something earlier in the story need to be clearer? Does plot complexity need to be simplified? Are the readers tracking the main tension? Conversely, rather than take a note that initially strikes her as clever, the writer must ask herself if the change might require further adjustments throughout the script, perhaps creating more problems than it solves.
No note or suggestion can be taken at face value; the writer has to work and sift and ponder.
Ultimately, the writer comes up with a game plan for the rewrite. This often takes the form of a new beat sheet or treatment to organize all the changes. I like to use colorful index cards and map out the entire revision on a 5'x5' cork board on my office wall.
This could mean handing in the script to a professor, delivering the script to a studio, passing it out to a writer's group, or just showing the pages to Mom. The important thing is that this should be the writer's best attempt at a "finished" draft. But alas, no script is ever finished. The writer will get notes, and return to the collection phase as he gets more and more feedback... ...and the cycle is repeated, again and again and again.
This Rewrite Process begins with the first draft and goes on with the second and third. If the writer gets a manager or agent, they will also get notes. If the screenplay is optioned or sold, the buyers will have additional thoughts and the cycle continues. If an actor or director is attached to the project, they will have new suggestions. As the project goes into pre-production, adjustments and compromises will need to be made due to budget, schedule, unforeseen opportunities and unmitigated disasters. As the project is edited and re-shot in post, further changes must be made. The script will likely go through rewrite after rewrite, churning through the cycle, all the way up to the premier.
The better the screenwriter can navigate this process, the faster and more effectively the writer can move through this cycle again and again, shepherding the core story so that each loop improves and clarifies the work, the better the screenplay will be.
What I have found is that not only do effective screenwriters work this cycle, but that they work on multiple projects at the same time...
Red - Ideas Screenwriters collect ideas while in the shower, driving their car, or reading the paper. They collate these ideas, sift through them and mull them over in their offices. They execute and present these ideas to friends and collaborators, usually over drinks and coffee and get feedback. They always have a bag of ideas brewing.
Blue - Pitches and Treatments Simultaneously, the writer is working on ideas that have been fleshed out into treatments and worked up into formal pitches. These too are distributed and rehearsed, tweaked and re-imagined, presented to buyers and collaborators, only to get more feedback and more loops in the cycle.
Green - First Drafts and Spec Scripts While ideas are brewing and pitches are performed, the writer is simultaneously polishing and rewriting completed drafts, hoping that just a few more turns of the wheel will make it good enough to sell.
Pink - Scripts in Production Simultaneously the writer is working on projects that are actually in production. These could be short films, indie features, webisodes, or the current episode in a TV series. These projects are getting feedback from producers and directors and unit production managers, and the script is changing to fit the reality of filmmaking on the ground.
So, when one stage is done, another begins. Once a film is made, the writer must be ready with a new script. Once a script is sold, the writer must be ready with a new pitch or treatment. Once a pitch is abandoned, the writer must be ready with a new idea. All these cycles have to happen simultaneously.
Software engineers will recognize the screenwriters' rewrite process as just a specific example of a general feedback loop, one that can be applied to any creative endeavor.
A recent article Wired Magazine, Harnessing the Power of Feedback Loops, suggested that feedback tools can be used to make just about any human activity more effective.
But as I am only a screenwriter, not an engineer, a psychiatrist or a cognitive scientist, I'll just leave it at this... "all writing is rewriting."