There are only two things to establish about a character from the outset–gender and age. Laborious, pedantic descriptions about specific physical attributes, cars and pets, musical instruments played, should be avoided. If a characteristic is crucial to the story, state this succinctly. If, for example, one of your characters, say, Ben Brandt’s graceful movement somehow ends up saving his life then foreshadow this in your description of him: Ben Brandt was built like an army barracks shithouse but moved with the grace of a ballerina.
Lengthy, unmotivated descriptions slow the forward thrust of the story and betray the writer’s inexperience.
So why do so many writers include them in their screenplays? Because it is far easier to describe a character’s varied physical attributes and traits than to reveal them adroitly through dialogue and action in a scene.
Reference to physical stature, hair colouring, and weight, therefore, are only relevant if they foreshadow aspects of the plot, such as the stutter that causes the murderer to trip up at the end, or the lack of height that motivates a man to over-achieve in other areas.
This extends to emotional traits as well. Indeed, one of the best ways to make emotional and physical traits germane to the story is to interweave them and have them explain some future aspect of the character’s action(s).
This brevity of description extends to the novel and short story too, for much the same reasons. In her wonderful book on the craft of the short story, Inside Stories for Readers and Writers, Trish Nicholson offers us several examples of this skill. In Modus Operandi she describes a character’s physical size: “A big man, too–he had to duck under doorways. His hands were as wide as dinner plates. To see those long fleshy fingers you’d realize the strength in them.” This description is not only germane to the story but it foreshadows menacing aspects of the plot.
Character descriptions should be brief and germane. Describe only those traits of a character that serve as triggers to the plot, and do so succinctly.