There are a number of people in Hollywood who get a lot of parts written for them. There is Mike the tough-guy biker who wears a leather vest, isn't smart enough to tie his shoes (wears boots), and has a girl friend as smart as his boots, (named Boots). I'm sure you recognize him. There is Ahmed the cab driver who can't speak English and always takes the longest route. We all know Ahmed and can recognize him on the street. Ernestine the waitress dutifully fills your order in your lap. We would recognize her in any city. Marsha the overprotective mother never lets her kid go out without boots on, even when the sun is shining.
These aren't real people of course, they are stereotypes. We could rename Mike, "A" and just put A in the script whenever we need someone like him. We always know what to expect from them because they are always the same. But that's just the problem, audiences want surprises. They want to see unique, original people who do unexpected things.
Archetypes are a special case. Mothers - nurturing people - are archetypes. Gods, angels and devils are archetypes. The policeman on the corner, doctors, nurses, teachers, scientists, and other authority figures are often archetypes, especially if they make brief appearances. These are people from whom we know what to expect. There is very little characterization and history needed for these. But even archetypes can be made unique by giving them personality, attitudes, a mission.
1) Give your characters a past, desires, problems - a life - just like other people. They will come right out of that stereotype.
2) When you find you are having your character do the same old tired things other characters do, push yourself to have them do something unique. You'll be pleased with the result.
"Non-dimensional" is a term applied to characters who have limited dimensions to their personalities. The writer needs someone who is angry, so that is the only dimension which comes through. Take Jerry the comedian. What things come through in his personality, and what other interests does he have? Is he a comedian all the time? Is he always kidding around, or dead serious? When his daughter tries to kid him, does he react angrily? Does he spend his time at the horse races, or building an MG car from a kit? Is he constantly encouraging his daughter to do well in her first year of junior college? Is he hot tempered when he or a member of his family is insulted? What does this do to his performance on stage - make it better or worse? There are many dimensions to Jerry to explore which would add to a script.
1) Know the things going on in your character's life and explore them. Use them to modify your character's behavior. Real people have spiritual, psychological, social, physical, and physiological dimensions.
We all speak "television" English, so how do you give your characters a voice? Speech mannerisms are one way. People tend to reflect their background. Once in a while you meet a guy pumping gas who speaks like an English Lord, but mostly they don't. If the guy pumping gas speaks like he is well educated, that's the audience's clue to watch for more from this character. Otherwise he probably speaks with less polish: uses more common word choices, possibly more four letter words, often more direct and less diplomatic, with conversation limited to the task at hand or the weather (except to his friends).
Dialect, which includes word order and word choice, is another way individuals differ. You have to listen to speech patterns in order to effectively portray this. Compare: 1) "God, I'm so tired, Elizabeth! Let's go home." 2) "I'm plum tuckered to the bone, 'Lizbeth! We best be gettin’ on home."
Most likely your story will have several people from the same social, economic, and educational backgrounds. They will speak much the same. The main way to differentiate them is through their choice of subjects to talk about, their motivations, and their point of view.
1) Use individual differences to give each character a voice of his own.
2) Avoid misspellings to indicate ethnic or geographic pronunciation, as in "gettin’ on home," used above. It is the actor's responsibility (and their coach) to create the proper accent.
3) Avoid extensive use of foreign language. It confuses the reader and audience.