Today, the question on my mind is one of tone, primarily the axis between ridiculous humor and the most unrelenting of serious works. As to the far ends of that axis, I know virtually nothing of it - I find shallow, silly comedy unappealing as a reader, much less a writer, and there's only so much grimness I can take before I feel the urge to lighten it up.
But there are a lot of gradients in between, as well as variants in the style of humor (and the style of serious, too - but humor is more fun to talk about). Even a dark, hopeless story may have moments of unexpected laughter. Many a tale that cannot be classified as comedy nonetheless has a running thread of character banter. And then, of course, I feel that you can't write a truly entertaining comedy without real stakes, real emotion ... a reason to read beyond just waiting for the next joke.
As far as my own writing, most of the time I fall towards the serious end of the spectrum, livened up by character commentary and the occasional oddity in the setting. Even assuming a "normal" world with no comic premise, there are always bizarre, funny and entertaining moments - and their very rareness helps them stand out. A bumbling official, a bizarre law, an unfortunate mishap ... all fair game without altering the tone of the story.
When I indulge in humor, it's most often a somewhat subtle, snarky brand of it, and it frequently sneaks into the style of the prose. The phrasing and choice of metaphor brings the humor as much as the content. When I write comedy, I look at the world slightly askew, exaggerating assumptions and starting from places that are - mostly - logical ... then take them just a bit further.
To repeat a point above, my favorite kind of humor is character-based humor because it can thrive regardless of the story's tone. Whether the characters themselves make jokes or the humor comes from the anticipation of how X will react to an event barreling down the pike, it has a lot of applicability.
At the same time, I love comedy that starts with a humorous premise and takes it as far as it can go: Thursday Next, much of Pratchett's work (I am thinking particularly of Going Postal here, which examines the entire concept of the postal service under a ludicrous microscope) and I have to point out Patrick Weekes' The Palace Job, which does the heist movie as a fantasy novel. What separates great comedy from an entertaining read to me is this ability to extrapolate even further - the worldbuilding of it, as it were. My personal foray into this field is "Who Wants To Be A Hero?" which is basically what would happen if the Greek gods had invented reality television competition to amuse themselves.
But once you've started with a crazy premise, it colors the overall tone of the work. That doesn't mean it can't be dramatic, exciting and even heartbreaking - take a look at Laura Resnick's Esther Diamond novels for a fantastic job of this; Doppelgangster is probably the only book that made me howl out loud and tear up, both of which are extremely rare occurrences on their own - but it does make it difficult to do anything that doesn't hang out its shingle as a comedy.
There was once a challenge on fantasy-writers.org to write either a serious story in a silly manner or a silly story in a serious manner ... oh, you can guess which I tried and which was insanely hard. I ended up deciding to go back and plug humor into it again, but discovered even that was difficult once I'd started in a serious vein ...
This whole topic comes up in my mind because the still-untitled story I'm finishing up has a rather light (if not silly) premise: a royal competition for hairdressers. I'm writing it rather straight, but there's character banter and a lot of snark in the narrative / descriptive passages. My hope is that it comes off humorous without being in-your-face funny ... we'll see.