I’ve decided that this needs to be my new motto. It’s related to “show, don’t tell,” but it’s a specific variety of the problem.
A common problem I see in manuscripts (many, many manuscripts, not necessarily ones I’m working on now) is a “tell” later in the manuscript that ought to be developed more as a “show” earlier. A great example of this is the relationship between two or more characters. If two characters are close (or if they fight, or whatever), don’t just tell the reader at a crucial time several chapters in that they’re close–have them interact in-scene, showing that they’re close in how they relate to each other. Then those “tell” moments later will come naturally and have a lot more emotional impact, both on the characters themselves and upon the reader.
So remember: If so, show.