Narrative, a question

Hi Everyone...

I'm learning...  

When I write I enjoy writing dialogs but I'm not clear on the basic structure of a conversation between two people.   The structure I most often use:

"Hi,   so how are you,"   Susan asked.

"Fine,"   Brad answered.

I would like to experiment with something a bit more dynamic, simplified  and professional but I don't have a clue on how to begin.   Can anyone cite an example.   I'm creating a story that has a lot of dialog.

Hugs
Mary Beth