Dialogue is something a lot of blossoming writer’s struggle with due to the variety of techniques and approaches. I find the possibilities for successful dialogue endless. On the opposite end of the spectrum, there are many ways to create bland, unrealistic dialogue. There are a few basic rules to abide that will ensure your conversation is received as an authentic representation of the interaction.
1- People do not speak in perfect grammar. Although you may be tempted to keep form and write the entirety of your dialogue as such, remember that you are trying to convey real people discussing a real topic. For practice, pay close attention in conversations to witness how inelegant and stylized human dialogue actually can be.
2- Carefully emphasize the dialogue with descriptive words that explain how someone said something. Every utterance we speak has a tone or inflection that informs others how we are feeling. We do not strictly say our words. People whisper, shout, guess, explain, reprimand, etc., the list is endless.
3- When someone speaks, they also display their thoughts and emotions through actions. Some people move their hands constantly; others are very rigid and stoic. For most of us, the action directly relates to what we are saying. Pair the dialogue with appropriate gestures and movements that coincide with the words when necessary.
It should be noted that not every line of dialogue needs the aforementioned accoutrements. Some sentences are straightforward, lacking any verbal or physical emotion. In that case, just writing the line will suffice. Be sure to practice dialogue so you can get the gist of how to convey different meanings. You could even follow the expression map and focus on specific emotions that arise in conversation. Another option is writing down a real life discussion and see if you felt the same while having the talk as you do after reading it on paper (a variation of this exercise would be copying television or movie dialogue onto paper and assessing its effectiveness).
Discovering which route works best will provide a practice outlet that ultimately leads to entertaining and believable dialogue.