While some authors set out with the idea of a series in mind, others are pleasantly surprised when they look back and realize that the novel they have worked on for months or years has the potential to become an entire series.

But how do you know when you’ve created something that can work as perhaps two books (think the Six of Crows duology by Leigh Bardugo), three (like Tomi Adeyemi’s Legacy of Orïsha trilogy), or even more (Rick Riordan’s Percy Jackson series, for example)? Here are some questions and specific circumstances to consider when potentially creating an extended literary universe of your own.

Is your protagonist complex enough?
Your novel’s protagonist is always going to act as the backbone of your novel, and this proves even truer if you decide to draw out that standalone book into a series. This means you have to demonstrate that they have the ability to adapt and undergo some serious emotional growth as events unfold.

Now, whether that growth is positive or negative, that’s entirely up to you, the issues you want to raise, and the point you want to ultimately make. Think about the flaws of your character (we all have them!) and how they can serve to further both the story itself and the character. What about your character is unique? This could be anything from a special superpower or a knack for getting into trouble. At the end, you have to make sure there’s enough there to keep readers coming back for more.

What is the genre of your novel?
While it’s technically possible to create a series out of literally any subject matter, there’s no denying that certain genres lend themselves to a series format better than others. Think about your own favorite book series. Chances are it falls into a category like fantasy, mystery, or science fiction. That’s because these genres naturally generate the immersive cast of characters and place that can really drive a story forward.

And it is truly the combination of elements that are needed—a defining quality of literary fiction is a compelling main character, for example, but there are not as many series that fall into that genre. Why? Usually those novels conclude the protagonist’s emotional arc within a specific span of time, which would make revisiting that character later feel somewhat redundant.

Are your characters likeable enough?
Now I don’t mean that all your characters have to be completely likeable all the time. In fact, that would make for some not-very-complex characters, which we’ve already established is a must. But there does need to be a healthy cast of people—not just the protagonist—with whom your readers want to spend more time.

You may create a bunch of flawed and interesting characters whose quirks and antics could potentially fill a twenty-book series. But if you don’t create a certain level of likeability for most of them, audiences are probably not going to stick around.

Do your characters have enough potential conflicts?
Just like you need protagonists with enough internal strife to fuel the emotional growth required to make them truly interesting, so your book needs to have enough external problems to make the book’s existence worthwhile.

Many fantasy novels do this by creating a brand-new enemy in every book, which is largely why that genre is so suited to a series format. Even when a threat is neutralized by the end of one book, it is important to leave a hint of some lingering issue (whether physical or psychological) that can be carried on to the next one. This gives the series a feeling of continuity, even if the majority of the conflicts change from one novel to another.

Is your setting inviting enough?
With all this focus on characters, it can be easy to forget that the place in which you set your potential series is arguably just as important. After all, a setting can be a character in its own right! It should ultimately be someplace in which readers can completely immerse themselves.

While this often includes building worlds from scratch—perhaps the best example is J. R. R. Tolkien’s beloved Middle-earth—it doesn’t have to be that wide ranging or epic. Think a small, picturesque town where mysterious murders happen or a coastal beach community where romance constantly brews. This vivid sense of space and place can lend a comforting feeling of stability to the series that helps readers know what to expect (at least partially) when they return to it.

A few notes
If you do decide to make your novel into a series, keep in mind that the first book should still be able to act as a standalone. While it may seem clever to end on a major cliff-hanger and force readers to wait for the next book, the truth is that you risk alienating them from ever wanting to pick up a book with your name on it again. That’s not to say that you can’t leave some minor points up in the air that can be addressed later—just make sure you resolve the main conflict in a satisfactory way.

Another reason this approach is advisable is that traditional book publishers will rarely purchase a manuscript from a brand-new author that doesn’t wrap up within one book. That’s because optioning a series is often considered too risky (though not completely impossible). If you’re going that route, you’re better off branding it as a standalone novel with series potential and leaving the door open for future discussions.

Andrea Moran lives outside of Nashville with her husband and two kids. She’s a professional copywriter and editor who loves all things books. Find her on LinkedIn.