Anyone who has ever read anything about writing or editing knows that there are two universal truths: 1) Show everything, tell nothing, and 2) Avoid adverbs like the plague.
The problem in writing a novel, is that by definition you are telling a story. Television, picture books and comics literally SHOW much of the story, but in the printed word everything is telling. So really, rule 1 is a fallacy. There are, however, degrees of telling, and the purpose of this rule is to nudge us towards the show-y end of the spectrum. For example:
Sarah felt embarrassed
Is more tell-y than
Is more tell-y than
Sarah’s face filled with an unmistakable tint of red
All these examples say the same thing, and since none is accompanied by a picture, they all do it by telling us what happens. The difference is that the second two paint verbal pictures.
If you’re editing a draft, you can do worse than to search for the word “felt” and check around it. Emotions are generally easy to fall into the trap of telling rather than showing. Although, “Sarah felt a prickling warmth in her cheeks” would be a decent way to deliver this sentence, because it’s using “felt” in a physical sense and not an emotional one.
Adverbs (and to some extent adjectives) are also often markers of telling, handily linking rule 2 in with rule 1. “He squeezed tightly through the hole”, the adverb tightly is arguably redundant because of squeezed, but it is also at the telling end of the spectrum. Instead, we could replace the sentence with something like
The skin on his arms grazed against the panelling; the hole was no wider than his shoulders.
Telling is often a shortcut. Showing almost always takes more words. As such, sometimes telling can be useful. “He slept soundly” could be replaced with “He lay in bed, unmoving, his breathing shallow and regular, his eyelids flickering only occasionally as a dream crossed his mind’s eye without disturbing his body’s rest”. But imagine if it was important for the reader to know that this continued for the whole night. I think most readers would vote to be told that, and not to have to read a minute-by-minute account of it.
However, if it’s not important for the reader to know the exact time period, it’s worth considering whether the reader could be left to infer that this state of affairs continued until the next scene, where we see the character awake and alert the following morning.