I recently did a series of workshops with students ranging from grade 4 to 9 tackling various aspects of writing craft: story structure, hooking a reader, character development, and a general introduction to screenwriting.
In discussions with the teachers, before or after my presentations, a similar issue was brought to my attention - the misuse of dialogue in their student's short stories. Dialogue rambled, was too "every day", failed to reflect character personalities, there was too much, or too little for it to be effective. I got the sense the use of dialogue in creative writing might therefore become discouraged.
And this information made me rather sad. My writing has always been dialogue heavy, likely why I was attracted to screenwriting in the first place, and, frankly, some of my best lines are words my characters say - not description or action sequences or heavy internal monologues.
Which is why I tweaked my workshops to include a segment on dialogue dos and don'ts. I flipped through my personal collection of writing manuals, googled the topic, scanned YouTube videos, and tossed my own ideas into the mix. The result is a two-page document I'm hopeful teachers, students, and writers will find handy. The PDF version is available HERE.
I believe the key to great dialogue is knowing your character motives / goals / beliefs / values / desires and how that knowledge will influence what they choose to say or leave unsaid. Then make sure what the character wants, in any given scene / interaction, comes through loud and clear. If their goals clash - all the better - your characters will challenge each other, contradict each other, and more importantly try to influence each other to see the situation they way THEY want it to be seen. Instant tension. Instant buy-in from your readers. If you do it right.
Below is a clip from the film The Knight's Tale. I highly recommend reading the script which you can purchase here, The Knight's Tale Shooting Script. Watch the clip and evaluate each character's dialogue. They know what they want and they aren't afraid to say it. Observe how the main character, William, wins his friends over. Bonus - this scene also sums up the theme of the film...anyone can change their stars.
Great dialogue. I know you can write it too.