Description may seem to be the least important part of your screenplay, yet scripts are read before they are filmed, and therefore well-written description is nearly as important in a screenplay as it is in a novel. Here are some dos and don'ts to consider as you are fine-tuning your description:

Do keep it short. Long, unbroken paragraphs of description will slow the pace of your script and annoy busy executives and readers, who will likely skim those same sentences you have spent so much time laboring over. It is not necessary to describe locations, characters or objects in minute detail. All that is necessary is a flavor. For example, for characters, it is enough to provide the gender, age range, and one or two effective adjectives or phrases to give us an idea of who this person is and why we should be interested in them. Ethnicity and any other physical traits are not necessary unless they are integral to the story. There is a practical side to this sparseness in character description: you want to make the role appealing to as wide a range of actors as possible. Similarly, with settings, it is enough to say that a room is messy. There is no need mention every pile of old magazines, crushed soda cans and dirty ashtrays. Leave the details to the imagination of the set decorator.

Do add white space. If you have a descriptive passage that is necessarily long, like a battle scene, then break up the action into several paragraphs, none more than five or six lines in length. This will make the description easier to read and move faster. However, even in action scenes, there is no need to spell out every beat. By the time the movie is made, a host of technicians and artists will have joined together to choreograph any complicated visual sequence.

Do break up sentences into shots. You can imply camera directions via separate sentences. For example, "Chuck looks at his watch. It's 11:17." The second sentence indicates a close-up on the watch without the writer having to write out "CLOSE-UP." Any change of angle or point of view should be indicated by a new sentence. "Hector slides into a booth, while across the room Sophie glances up and sees him" is not as cinematic as "Hector slides into a booth. Across the room, Sophie glances up and sees him." The latter works better in a screenplay, because the two sentences mimic the change in focal point and therefore imply a cut.

Do be expressive. Just because your description is short doesn't mean it has to be dull. Whenever possible choose apt, dynamic verbs and clever adjectives. Instead having someone walk across the room, have them march, stomp, trudge, dash or stumble, depending on what is appropriate for the scene. You want to bring the picture to life for the reader, and a few well-chosen words will do this for you.

Do try to emulate the tone of your script in the description. Description for a comedy should be wry and snappy. Description for a thriller should be tense and foreboding. Read produced scripts in different genres to see examples of how other writers have achieved this.

Don't use the passive voice. For instance, "Dave is hit by a falling brick" is less dynamic than "A brick falls and hits Dave." The latter comes across as closer to real time. The same is true of sentences like "Sheryl is rushing across the room when she is intercepted by Deanna" as opposed to "Sheryl rushes across the room. Deanna intercepts her." The second version makes the action feel more immediate and therefore a better translation of what we see on screen.

Don't include internal thoughts. It is fine to throw in a reference to how a character is feeling (angry, annoyed), although it is always better if you can show the emotion via action. However, avoid detailed mental processes: "Phoebe snatched up the knife, remembering how Joe had belittled her at dinner." Put in the description only what we actually see on the screen, and let the reader figure out the rest -- just as the audience will do when they see the movie.

Don't include camera directions. You may occasionally see camera directions in scripts by produced writers, but the practice is considered out of style now. Your goal is to write a script that involves the reader completely in your story, and constantly cutting away to give us a new camera angle interrupts the flow and ironically makes the script feel less like a real movie experience.

Don't talk to the reader. There are a few professional writers who are known for throwing jokes and asides into their description, but they have succeeded in spite of this, not because of it. Again, as mentioned above, you don't want to do anything that will take your reader out of the story. Corny or snide commentary points up the artificiality of the world you are trying to persuade the reader to believe in. The exception is when you are trying to establish tone. In comedies especially, writers may toss in a bit of witty commentary here and there. It has to be done exceptionally well, however, and sparingly, or else it will detract from your story rather than enhance it.

As suggested above, the best way to learn what kind of description works is to read scripts by produced writers. Note when a writer's description grabs you and, just as importantly, notice when it bores you. The more you read - and write - the better your description will be, and the more likely executives and readers will savor and appreciate it, rather than skip it.