Dialogue in fiction is not like dialogue in real life. In real life, our conversations are filled with expressions like “um” and “Ya know?” that have no place in fictional dialogue.
So how does one write fictional dialogue? Fictional dialogue can be described as “distilled” in the sense that it consists of the essential words used in real-life dialogue. Fictional dialogue rarely uses “um” or “ya know” unless doing so is critical to revealing your character.
In order to write outstanding fictional dialogue, practice listening to the age group or the audience for which you are writing. Then take what you hear and “distill” it for use in your stories.