Many writers advocate that simply eavesdropping on other conversations is one of the best ways to learn how to write dialog. Finding a cafe, restaurant, or other public place can be a great way to study these every day interactions.
Teenagers have provided some of my favorite lessons on writing dialog. Their excessive volume makes them easy to hear and their excessive drama provides a wide range of emotions and situations. I never integrate such conversations into a story, but I hear them in my mind while writing similar dialog.
Ed Cyzewski: Author // Contemplative 