Plot vs. Character
Plot Vs. CharacterThese days (in Hollywood at least), most scripts are plot-driven, though a few (independent or "art" films) revolve around character. As a general rule, "classic" movies interweave plot and character so deftly and thoroughly that there's no easy way to separate the two. In The Godfather (Parts I & II), for example, the plot of Michael Corleone's struggle to power unfolds in perfect synchronicity with his slow and steady corruption, and there is no way to say which came first or took precedence in the writing, because there is no separation between plot and character. Character is the means by which plot unfolds, and plot is the way the characters develop and reveal themselves. This is a very rare case, but it serves as a good example. It's not necessary to achieve greatness to learn the lessons laid down by it.
In practical terms, when starting on your script, it may be enough just to ensure there is no actual conflict or discrepancy between the story and the characters. Don't try to force round pegs in square holes by having your characters do things inconsistent with the way you conceived them, simply in order to keep the plot moving. (E.g. Cheap horror movies in which the characters do incredibly stupid things in order to put themselves in danger.) On the other hand, don't get so wrapped up in developing your characters (whom you are likely to have a soft spot for) that you neglect to move the story forward. Even in novels-when the author has the luxury of interior monologue (the movie equivalent of this is narration, a device to be used sparingly), it is a well-known rule-"show-don't-tell"-that characters should reveal their fears and desires through actions, not merely through thoughts. As with The Godfather, when characters reveal themselves through actions, you can be sure we are seeing and not "hearing" what the characters are made of. Story develops through character, characters reveal themselves through action. Hence, action is the basis of all good storytelling.
How Characters Develop Through the Course of a StoryIn most cases, you are likely to want to focus primarily on plot, and only secondarily on character. Hence it is not only permissible but advisable to draw your characters as roughly as you can-function within the story, job, age, etc-and only once you are writing start to develop the quirks and nuances that will give them a life of their own. If you are telling a story, for example, about a young man returning to his hometown to visit his sick father who gets embroiled in a murder mystery (Blue Velvet), you don't need a complete psychological profile of your character: what the story will put him through-as in life-will reveal what he is made of.
If your story is imaginative enough, it will shape and define the characters as it proceeds. This is the case with any plot-driven script: not that the characters are secondary (though in genre works such as The Matrix, this is often the case), but that they begin life as functional and by the end-if your story is told properly-will have assumed autonomy. Such characters are the engine that drives your story, and you may not get to know them except by their effects. (But if you find your story breaks down halfway through, you are going to want to give your characters a good looking over.)
Autobiographical WritingIn the case of more autobiographical scripts, you may decide to make do with a situation rather than an actual plot (as in Annie Hall for example, and much of Woody Allen's work). First-time writers who want to shoot their own films on the cheap often write just this sort of script (for practical reasons), and here character takes obvious precedence over plot. The proper approach is then the reverse of that described above: rather than characters being functional to story, the story serves to reveal the characters.
Here the writer invents situations in which his or her characters can interact in amusing and/or gripping ways in order to involve the audience. There are plenty of comedies in which plot is at best functional, at worst arbitrary and absurd, and the only concern is for putting the characters in hilarious situations, to act in absurd or riotous ways and deliver snappy dialogue. Unless you are planning to write an Ace Ventura or Austin Powers (or Airplane!) kind of movie, however-in which neither plot nor character amount to much and laughs are your only real objective-it is probably wise to take a leaf out of Woody Allen's book and do away with "plot" altogether. Annie Hall was basically a series of scenes about a relationship and eventual break up; when Hal Hartley plots his films, he makes it clear the story is merely a there for the characters to interact in, and the effect is pleasingly ironic and (unlike Airplane!) perfectly sophisticated. Likewise, after a very different fashion, Kevin Smith often lets his characters do most of the work of the "story." (An extreme example of this would be Linklater's Slacker and Waking Life.)
In such cases, the plot takes a back seat and the dialogue carries the day. By concentrating on the characters and the best way to develop and explore them, the "plot" can happily reveal itself to you as you go along.