Context First, Subtext Second
Subtext, especially good subtext, can be tricky to write. But in order to write good subtext, you need to have context first. And in order to do that, you need to understand the difference between them and where each one fits in storytelling.
Some writers make the mistake of trying to make the context into subtext. This is a problem for several reasons, one of the main being that it makes the story very vague. In vague writing, the audience can't really tell what is going on. Without proper context, they aren't sure how to interpret information and actions. Often, this sort of writing manifests when the writer is trying to follow the "show, don't tell" rule too religiously, which usually leads to writing that is too cinematic.
However, creating context does not necessarily mean you have to "tell" straight-out all the time. It can also come from taking advantage of connotations, words with specific feelings attached to them. With that said, though, it's impossible for most stories to have proper context without some telling.
Context reassures the reader that they are in the hands of a good writer through validation and helps them interpret what is happening in the story.
When there is little-to-no context in a story, the reader (subconsciously) can't tell what is intentional or what is a mistake. For example, if you have one character call the other by the wrong name, but give us no context, we don't know if that is a typo or something intentional. And if it's intentional, we don't know what it means.
Mack shut the Hummer's hood. "Should be fine now," he said to John.
"Great. Thanks, Karl." John got in the driver's seat and stuck his key in the ignition. The Hummer roared to life.
John headed for the main road.
This creates a few problems in the reading experience. Because the audience isn't sure how to interpret John's dialogue, they'll be stuck thinking about it longer than they should be, longer than it deserves. And they'll be waiting for an explanation, and they'll want it quick. As they continue reading paragraphs, the tension builds up in the back of their minds, but it's not the good kind of tension. It's not the kind of tension that makes them eager for more of the story. Instead, the tension comes from them not being sure they can trust the writer. The tension comes from them not being able to tell if John calling Mack, Karl, is intentional.
If it was a mistake, it shouldn't be there. It should be edited out. If it's not a mistake, they have no context for how to interpret it. Is this supposed to be a character trait? Showing that John has difficulties remembering names? Or is it meant to show that John is a jerk who calls people the wrong names to get under their skins? Or is it meant to show how nervous John is about talking to people?
We don't know because we don't have any context. It's vague and could mean any number of things. The reader is stuck trying to figure it out.
This can happen when the writer is trying to make their story mysterious, exciting, or engaging by leaving room for readers to come to their own conclusions and interpretations. They are right in their desire to have the reader participate, but it is misplaced. This is a job for subtext.
If the writer is not going to give the reader a clear interpretation right away, they need to validate the readers' concerns. The writer needs to clue them into the fact that this is intentional, so the reader isn't stuck trying to appraise the author. If something strange happens, and the audience doesn't know why (because it will be revealed later), they need their confusion or skepticism validated, so they can stay in suspended disbelief. They need the writer to say, "Hey, I'm aware this is strange, but it's intentional, hang in here with me."
When handled right, this may actually strengthen the audience's trust in the writer instead of weakening it (as long as they believe there will be a proper payoff for waiting).
Context gives the reader something to grasp onto, it gives them a sense of grounding, so they can be participators through subtext. If there is no context, there is almost no investment in the story, because the audience doesn't have access to the meaning of any of it. If they don't have access to any clear meaning, they are unable to care about what happens. The only way the audience can be invested in it, is if they are invested in the author--they trust the author will bring context later (and it MUST be brought later, not left uninterpreted).
This sort of thing usually only works in very short passages. For example, if you peruse the bookshelves of a bookstore, you will probably find prologues that lack context. This is because the prologue is acting as a teaser for the story to come. Readers trust that the context will come later, but it must come. At some point some context must come to explain the teaser. You may also see teasers as very short chapters or scenes. There is a reason teasers are short. It's because they lack full context. Audiences will not want to sit through a 50-page teaser. Can you imagine sitting in a movie theater and watching a 20-minute teaser for an upcoming release? Teaser trailers don't give you much context; they work off snippets of promises and emotions. A 20-minute movie teaser would leave you making a mental to steer clear of the release.
When you don't have context, you don't have tension. A vague mystery may hold readers for a little while, but if they don't know how to interpret what they are seeing, they can never get invested enough to experience tension.
Context can change and shift. Context can be ambiguous (which is not the same as vague). But context needs to be there. A story should rarely be vague, unless it is absolutely 100% intentional and serves the content. (And note: context is not content. Context is what helps us interpret content.)
Context is an invisible hand that guides the reader. It clues them into meaning, interpretation, and the boundaries of those meanings and interpretations.
Here is my earlier example with context added through telling:
Mack shut the Hummer's hood. "Should be fine now," he said to John.
"Great. Thanks, Karl." John got in the driver's seat. He loved calling people the wrong name, just to get under their skin. It afforded him a power over others that was subtle enough to get away with.
John stuck his key in the ignition. The Hummer roared to life, and he headed for the main road.
Here, the context quickly validates the reader's confusion of the wrong name and clues them into how to interpret it. It also immediately makes John a more interesting character. It's likely readers, even if they don't like or agree with John, will want to know more about him. He's so strange. He's so unique. And maybe a bit dangerous. The readers become more invested in the story.
See, telling is not always a way to kill a story. When done well, it makes the story better, more interesting.
Now, you can also provide context through the right connotations. In my example, that probably won't work. Remember, the more unusual the behavior or information, the more likely it will need to be handled with some telling (largely for validation). The more likely it can be misinterpreted as a mistake, the more likely it needs to be addressed (more) directly.
But situations aren't always as strange as John calling Mack the wrong name. If you are writing speculative fiction that takes place in a different world or has an "insider" as a viewpoint character, your reader will need context to ground them into what's normal and what's not. Sometimes this context can simply comes from how other characters react, the way new terms are handled in the text, and the words associated with those terms. Sometimes context comes disguised as some good dialogue or a character's deep thought or feeling.
But context is different than subtext. Before you can play with subtext, you need some context. If the reader isn't grounded in context, they can't really access subtext. Remember: context first, subtext second.
Once the reader has some stability, some grounding with context, you can make them a participator--you can create mystery, amplify tension, and make the story more exciting and engaging. Once readers are invested enough you can make them investors for real. Context can play into subtext, and vice versa, but enough context must be present before you get creative with subtext.
The elements of the story that ground the reader must almost never be treated as subtext. For example, the basic setting should not be treated as subtext. Actions characters are currently taking, such as helping someone off the bus and to a park bench, should not be treated as subtext. Anything the reader needs to have access to, to understand the basic, surface of the story, should not be subtext. In my article on undercurrents, I explain the different levels of depth a story may have. Subtext is fantastic for deeper currents, but it should (almost) never be used for surface material. Using it in that way is almost an oxymoron; subtext is meant to give us (limited) access to deeper underworkings, not to try to put surface material in the undercurrent, so we can't see and understand them (vague writing).
In context you gently guide readers so they can follow the story. In subtext you guide a little less, letting readers interpret what is happening and coming to conclusions within themselves.
To understand, discern, and learn how to write and handle subtext, read my post on it here. To understand and learn specific techniques to handle mysteries, read my post on it here.
Vague vs. Ambiguous: Which are You Telling?
Breaking Writing Rules Right: "Show, don't Tell."
10 Cheats to "Tell" Well
Validating the Reader's Concerns
How to Write What's Not Written (Subtext)
Crafting a Killer Undercurrent for Your Story
The Mechanics of Rendering Mysteries and Undercurrents