Okay, I am going to be frank here. I suck at this aspect of writing. Fanfiction ruined me. So poor Chester had to try and fix the mess I’d made of my own writing style. I’ve gotten to where I catch it as I’m writing half the time, and the other time I catch it during edits. I figure I had better explain a bit about what it is so it helps other people who might have the same problem.
Stimulus response is making sure that for every action, there is a reaction from the characters impacted by it. It doesn’t have to be a big thing, just a sign to show that the other character heard. Eye rolls, nods, shakes of the head, all count as a reaction, as does a character saying something in response (which in turn requires another response). It’s a giant game of tag, in a way.
There are a few cues that can tell you if you have a stimulus and response problem. For example, if you’ve got two characters present and you haven’t written any sort of action or dialogue from the second in two or three paragraphs, you’ve got an issue. Too much time has passed, they had to have had some sort of reaction to whatever the main character just did or said. Huge swatches of dialogue can also show you an issue. Think about how long you can stand to listen to one person yammer at you before you interrupt, and then time how long it takes you to say whatever the huge bit of dialogue is. If it goes beyond that time limit, guess what? You’ve missed a reaction.
There are also a set of keywords to keep in mind. If you use once, before, after, and some uses of as, then you’ve got an issue with your order. A reader wants to read things in the order that they happened. (Or so I’m told.) Sometimes those words are fine. But I recommend running a search for those words, so you can look at those paragraphs and making sure that things are going in the right order. Even though I think that I’ve caught myself using them, I know I’ve had times when either I’m tired, just trying to force the scene out, or putting words to the page to get unstuck where I slip back into the habit of mixing things around in an attempt to keep from sounding repetitive. There are better ways of doing it than just restructuring the sentence so you’re going backwards.
Another part of stimulus/response is the order of the reaction. The way I was taught was it goes emotion, thought, action, dialogue. You’re going to feel something from a stimulus, first and foremost. Sometimes a character will completely skip the thought step because the emotional response is so strong, and that’s fine. There are exceptions to this order, but if you think of it all in terms of a response, it helps make more sense. When a characters cuts their own dialogue off with an action such as throwing their hands up in the air or huffing their breath, it’s their response to their own words which is frustrating them. (I know this seems like nonsense, but it does help your scenes flow better.)
Most writers don’t pay attention to their structure, and there’s two reasons behind it. One is writers are under the assumption that their agent and their editor at the publishing house is going to fix everything for them. This is a lie. It used to be yes, they were there to help you out. But at this point in the business, most agents are retired editors who left the publishing houses to make better money, and while they’ll put in some work for you, they aren’t going to help you out that much. And when they lost those editors, the publishing houses didn’t replace them. So what editors they do have are overworked and overwhelmed. They are going to do a pure spelling and grammar check on your work, and that’s it. The second reason why people don’t worry about their structure is they don’t believe it’s important anymore. Stories and how to tell them are always evolving, and for many writers, stimulus/response and reaction order are old-school tools that aren’t needed anymore.
I’m sort of an inbetween on the second one. On one hand, I am not going to kill myself to structure a story in a particular way, and I am certainly not going to follow old pulp-fiction tropes about how my stories are supposed to go. On the other hand, I respect that keeping these old-fashioned structure rules in mind does two things for your story. The first, it helps cut down on your word count. You would not believe the number of words it takes you to mess the order up. While you do add words with missed responses, if you need to keep that scene below a certain order, you can eliminate some fluff wording elsewhere to make room for five words. The second, it helps the flow of the story and the scene. While you know what order actions take, your reader only has the words on the page to go off of. It can be a nightmare to keep track of what happened when with the stimulus response order all out of whack.
It’s helpful sometimes to think of things like a movie, in my experience. Trying to play a scene out like a film in your head can help keep the order straight, and keep track of the various responses. Focus on one-on-one situations first, since group settings can be a b-word in my experience, and build on them with more characters to practice. And if you flub it up, don’t sweat it too much. It takes work and practice to write, and we’re all works-in-progress.