Janet Evanovich has been quoted as saying this on the subject:
"Instead of stating a situation flat out, you want to let the reader discover what you're trying to say by watching a character in action and by listening to his dialogue. Showing brings your characters to life."
I think it's fair to think of "Show. Don't Tell" in terms of a job interview. In a job interview, unless it is on site and you're given specific situations to "show" what you can do, the interviewee is typically sitting across from the interviewer... "telling" what he or she can do.
Even better, think of a high school courtyard, two guys shoulder to shoulder, walking in circles. What are they doing? Mouthing off... "I'm gonna do this!" "I'm gonna do that!" I Hated (yes, that's a capital H) this preamble. I always wanted to yell out... "Don't Talk Me To Death! Whatchu Got? I'm gonna be late to class watching you fools!"
Now, as an author, I could write this scene and "tell" you how angry the guys were. Or how embarrassed Guy A was that Guy B kissed his girl. Or how nervous Guy B was that Guy A was a foot taller than his foe and twice as wide.
I could describe the biting embarrassment that stung Guy A's eyes every time he glanced at his soon to be ex-girlfriend. How his fists clenched tighter with every abrasive brush of his foes shoulder. How sweat pooled in his tightened palms. How his muscles flinched with each step. How he growled every profane word he could think of. And, how sweat beaded on Guy B's forehead, running into his eyes. How tiny quakes of uncertainty rippled through his body as he silently considered how many pieces his body would be ripped into. But, how he stood up to Guy A because no body else would. And, how the girl's love strengthened his own resolve, because after all she didn't love Guy A anymore. And, how he felt the girl's gaze at his back, powering him into certain massacre, yet for the best cause of all... her hand.
Showing, not telling is one of the best tools a writer can have in their toolbox. And I am happy to say that I am participating in a "Show vs. Tell" Blogfest over at