Take Jerry the comedian. There are many dimensions to Jerry to explore which would add to a script. Use them to modify your character's behavior. Real people have spiritual, psychological, social, physical, and physiological dimensions. 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. 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. Let's go home. We best be gettin on home.