I'm going to go out on a limb here and say that the first piece of writing advice most of us have ever gotten was that grand chestnut, "Show, don't tell." It's repeated in near constant refrain and here's the thing: It's only half-right.
This particular piece of advice crops up for two reasons. One, it's an easy shorthand for describing a pretty common problem and two, it's easy to remember.
But writing is not that simple. The advice is well-intentioned, but it has an inherent flaw. That is, that one is always supposed to show and never tell. And that's simply not true. There is a balancing act between show and tell. Show too much and prose drags, your pacing slows and readers can get...bored. Tell too much and the story move too fast, there's nothing there to stick to the ribs.
You can't take the advice as gospel but merely as a reminder to be more conscious. There is a time for you to show the moonlight streaming through the window and a time for you to say, the moon is full. (80% of the time I see people touting this bit of advice, they use that "moon glinting" quote. Like...all the time.)
Different genres have different linguistic styles. Different authors will have different styles within those genres. I write MG differently from YA and Adult and I certainly write historical differently from contemporary.
There's another term you may have heard through the years, purple prose. This is, in my opinion, showing gone wild. It's elaborate, extravagant, over the top. It's taking a page and a half to describe a picnic table before finally telling me that the table is on fire. It's saying a thousand things, burying the really important things in the morass of your descriptions.
When description begins to interfere with pacing, you know there's a problem and when your pacing is moving too quickly, you know you have room for description.
I know that seems ridiculously simplistic, but it is that simple. So here it is again.
If the pace of your story is moving too quickly, you need to add description.
If the pace of your story is moving too slowly, you need to cut description.
Or, to put it another way.
If the story is moving too fast, stop and show.
If the story is moving too slow, start telling.
That's it. That's the big secret. You know what else can speed up or slow down a story? Dialogue. But it still comes down to how you're writing that dialogue. Is it descriptive or is it pointed? Is it between two people or six? Complex ideas, complex sentences, they slow down the reader. Short sentences are fast.
And it all goes back to show vs. tell. This craft of ours has a thousand nuances. You can learn every rule, every word and piece of punctuation and you still won't have mastered the craft. Because the greater part of mastering this craft is finding your voice. Voice is a mixture of show and tell. It's your personal recipe of mannerisms and broken rules, how you show and how you tell that combines to create your voice.
Finding that balance, that recipe, is hard. It can be even harder when you're being torn in a thousand directions. When you're being told that there is the one true way and your way doesn't match. There is no one true way to write. There are elements. There are rules. And you have to decide if you're going to incorporate them, follow them--or not. Keep writing. Find your own way. Find your way.
Show and tell.