Summarized from the book 'Cinemanubhavam' (Cinema Experience) by Adoor Gopalakrishnan.
It is impossible for me to start shooting before the script is complete in all its aspects. First I should be aware of what the movie is about: the story object. This is the fixing of the story.
What ideas am I trying to convey through this movie?
That forms the theme
Then I need mind and bodies that can carry of this theme convincingly; strong characters.
All stories aren't apt for movies. There should be a narrative with characters and events. This narrative is the logical flow of events in the story.
After this comes the Treatment. Here we have to discuss all the events in detail. Even the minor characters should have their presence here.
Next comes the script.
It is the document of all what we see and hear once the movie gets into the screen complete with scene divisions and dialogues.
There are a lot of differences between scene divisions in a movie and a drama. In a play each scene is meant to raise gradually the dramatic tension to its climax. In a movie the scenes are divided by places and time of the events involved.
What is important in the scene descriptions is that the characteristics of the events as well as the actions of the characters should be there. Physical actions should be stressed from which the audience will be able to deduce the real character of the character. It is 1000% better than four or five characters commenting on the character ("He is a wonderful human being" or "He is a bad guy")
In the stories we tell our children they will always ask who is the good guy and who is the bad guy. And we tell them. Should one treat a group of matured adults the same way? That is offensive.
The primary rule of all writing appears here too i.e. Show; don’t tell.
Dialogues should be natural but not dryly ordinary. It should reflect the tension of the moment.
If the writer has known the characters (I mean their living counterparts) it will be easier (naturally) to make them believable.
The minor characters are important as well. It is not important to go deep into research into the background of all the characters. But the writer should have be aware of it while writing out a character.
A summarized translation of Adoor Goplakrishnan's article " Screenplay: An Introduction"
(This is a free translation, it bears very few resemblances to the original in terms of the style. I just summarized the ideas because I found them interesting )