In order to break the rules correctly, you need to know what they are and when and how it is not only okay but good to break them.

Good dialogue is a wonderful thing. It can grab a reader and pull them into your story. Your characters feel real when the dialogue feels real. Bad dialogue can stifle your flow. It can make your entire work feel unbelievable. It can kill your characters, pace, and story. What makes dialogue good though?

Source: Let’s Talk Dialogue: When to Break the Rules – Wordquill