Dialogue is quite simply the characters speaking to one another. Character A has a point to make to Character B. Perhaps they argue; perhaps they want to get a certain point across.

Good dialogue is more than just what the characters are saying. You should be able to discern the differences between characters by their dialogue. Men and women speak differently as a whole, but not all men or women speak alike.

How do you decide how to write good dialogue? The simplest way is to listen. Writers are notorious for eavesdropping on conversations around them, but this a good way to learn dialogue. Listen to how your mother speaks, how it is different from your father and brothers. Listen to your boss.

An educated person is going to speak a lot differently than someone who has never been to school. These are useful ways to make the dialogue sound unique for each character.

However, be cautious about the overabundance of dialect. Using a thick Scottish accent or a Southern accent over and over might get a little annoying after a while. At the same time you might want to include it the first time a character speaks so the reader gets the idea of how the character sounds.