The ideal dialogue has a combination of the following elements:
1. It moves the story forward. This rule actually applies to any element of a screenplay. Any piece of a conversation or comment or speech has to elaborate on the plot or reveal something about a character (a form of exposition). Throwaway dialogue such as “Good morning, Bob” has to be kept to a minimum or eliminated completely.
2. It is subtle and clever. Films are an artistic and creative expression. The last thing the audience wants is a trite or boring dialogue. The challenge here is to make a realistic dialogue sound clever and unique. Plus, the audience is smart, and they love to feel that way. So instead of spelling out everything for them, give them clues and allow them to piece it together.
3. It is witty or comic. The audience of movies and TV shows love to laugh, but such a feat is not accomplished easily. Comic dialogue must keep up with a character’s personality. And creating the right situation in which he or she says it is also challenging because, as mentioned above, any dialogue also has to move the story forward by either furthering the plot or giving exposition on a character. This is the reason why in movies people don’t just stop to tell jokes to one another. The gag must have narrative value.