Characters are not created simply by writing names on a script. Each should have a clear voice, and be easily recognisable. You have to get into the head of the character and if you write a small back story, it will help you to do that.
Character is made up of temperament, behaviour, attitudes, prejudices, inherited values, pressures, influences, upbringing and surroundings. This can be made more transparent if expressed by the way someone dresses, the kind of home they have, their friends, hobbies and the way they speak. Get to know your main character really well, his appearance, his habits and mannerisms, his motivations and especially his past.
Your reader must care about your character. They must be recognisable people with the same struggles, heartaches, triumphs and failures as is common to us all.
Use information sparingly. There should always be a little that’s still unknown in order to make the story move forward.
Don’t just have goodies and baddies. Every bad character should have a redeeming feature and every hero should have a flaw. This will make them into rounded people. And try not to have stereotypical characters. Starving painter, the stuffy professor, and the whore with a heart of gold… we’ve seen them all before and they are boring.
Be clear about your character’s motivation. Is it revenge, unselfishness, jealousy, true love?
If you give your character a mannerism, don’t overdo it. Allow your character should ‘grow’ within the story.
Be careful when choosing names. Agnes is old. Susie is fun. Daisy is a child. Jack is attractive. Rupert is rich and of course, after the film Psycho, what else could Norman be but a disturbed killer.