|Match tone with story and theme|
While the tone of a piece can vary somewhat by scene, it's best to be consistent throughout. A work can be satirical, ironic, somber, exuberant, even triumphant. Each tone has a spectrum, but it varies by shade, not color. An uneven tone leaves readers questioning the characters, the real point of the story and, ultimately, the writer's motive.
How do you find the tone that best matches your piece? One way is to distill the story into a log line — a description of the work in 25 words or fewer.
Here's an example:
A woman with Alzheimer's fears she won't get the chance to tell her estranged daughter she still loves her.
What's the action word? Fear. It's the heart of the story, and sets the tone of the piece. The log line also sets the story's context, because it shows whose tale is being told. Yes, the work is partly about the daughter, but it's mostly about the mother's fear of unfinished business, and important business, at that.
To find your tone, it's important to know your story and your characters, but especially to know the heart of the piece. The "this is a story about" core of it. Keep that before you, and you'll keep an even tone — and an even keel.
For more on this important element of fiction, see "The 3 Most Important Elements of Fiction Writing," by Magdalena Ball.