Dialogue isn't easy to write well. Last week I talked about it being one of the red flags that editors use to spot an amateur writer. Maybe it's because beginning writers use dialogue more as a vehicle to deliver information. They don't understand its primary purpose: to increase tension and emotion in a scene.
I learned dialogue-writing many years ago, via a two-step method that serves me well today.
Step 1: Learn to listen to how human beings talk--and how they don't listen to each other.
Step 2: Learn to pare down the real-life dialogue into dialogue that works on the page.