When I was in school, and when I was a beginning writer, nobody ever hesitated to offer up the #1 advice for fiction writers: "Show, don't tell."
I recently heard a radio ad for a cruise line - and it's obvious that they took this advice to heart. As a result, they created an entire advertising campaign that aims to transport the listener with their wordy descriptions, similes, and metaphors, with the sole purpose of selling more tickets for their trips.
But, while this may be sound advice for an amateur to help build good habits in writing, it is not always true in a professional setting. The cruise line did not create an inspiring advertisement - they created an overwritten mess that makes the listener laugh, rather than feel like they should be on a trip.
A good writer knows how to engage his audience and then keep them wanting more - and if everything becomes a detailed, flowery description when the reader feels the story is becoming stagnant, then the author has failed to use prudence in his work, and audiences will react. A balance between showing and telling is not an easy thing to teach, because it is like knowing the precise moment to take a swing at a baseball: it is something that comes naturally with experience.
However, it is not impossible to at least get a basic understanding of how this balance should look.
The main thing to keep in mind here is what your scene is about, and how you want the reader to react. For example:
"She stepped outside in her sapphire-blue gown and gripped the handcrafted iron railing. Her presence engulfed the belle epoch scenery, commanding all eyes to be on her. She took a breath, and lingered another moment to ensure she wouldn't wake up mid-dream. Then she started carefully down the stone steps, toward the man in the black tuxedo who was waiting to take her into forever."
"She walked outside, looked at the crowd of guests, then continued down the stairs toward her future husband."
The first example is flowery as can be, but it works in this case because the scene calls for the reader to take a step back and take in the scenery and the action in slow-motion. The second example, however, kind of leaves a bad taste in the reader's mouth, because it robs them of the romance of the whole scene.
Then there's this:
"Her fashion-forward style made her curves look like a painting from the Museum of Modern Art. She ran just like the other Beverly Hills girls do: slow and careful, so as to not damage her Manolo Blahnick shoes - but she was running for her life. There was a man oozing lust from his eyes about a mile away, galloping toward her like a race horse on a victory lap. He wore black pants and a long-sleeved shirt, and his brown hair bounced with each step. The knife in his hand glinted in the sun at intervals as he ran, and his breathing resounded through the walls of the alleyway. She knew she was in danger."
"She ran as quickly as she could, grasping for anything that she could use to defend herself. Left, right - she had no idea where her legs were taking her, where her desperation had led her, but she knew she had to run. Run, Lily, run, she thought. Her attacker, although older than her, hammered on toward her and made it seem to Lilly he was more than human, determined to satisfy some ungodly hunger to ravage her."
The first one here sounds almost comical, because the author is taking the time to describe irrelevant things that slow the action and are irrelevant to the fact that this woman is being chased by a maniac who probably wants to kill her. It is simply too wordy for the sake of being wordy - who cares what the two people are wearing?
The second version does a much better job of relaying the sense of urgency and the tension the protagonist is likely feeling because it uses rhythm, repetition, and brief descriptions of relevant things - the context of the scene is displayed in the text itself, rather than in the descriptions.
Showing, telling - it's all part of fiction, and both are tools in the overwhelmingly all-inclusive Writers' Arsenal. And, as writers, we must be able to utilize all of these tools effectively to create not just good works, but great works, and eventually craft the Great American Novel.