Should you write a series or a standalone? One has lots of moving pieces to consider, and the other feels out there all lonely with nothing to anchor it to.
As always, you should do what's best for you, but I have some thoughts on the pros and cons of each, and how they can work for you.
Standalones
Look, I have a whole workshop I’ve developed on why I think you should be writing series (more on that later), so I’m admittedly a bit biased here.
But I can see why standalones would be tempting—so much less planning to do! you can just start writing and not worry about interconnecting pieces! And I do think there are some times when standalones can work really well:
When you’re feeling experimental: If you’re trying something new—a new sub-genre (dark romance to sunny rom-com, or vice versa, for example), or something that just doesn’t really align with your current brand—a standalone will give you some freedom to stretch your wings and test out this new direction without sinking too much time and money into it, or confusing your audience with something unexpected from you. (Maybe do this under a different pen name?)
Novellas: This could also fall under experimental, but novellas are a fun way to try something new, again with even less of a time commitment. Or you could write a standalone novella for characters who don’t quite fit into any of your already-established worlds/series, but who are still very in keeping with what readers expect from you.
Holiday stories: People always love a holiday story, and it’s a great way for new readers to discover you without having to be already invested in your series and know who the other characters popping up are.
Specific niches: Some sub-genres just don’t really support a series model. In indie Jane Austen fanfic (JAFF), for example, almost everything is a standalone. Readers generally just want Darcy and Elizabeth together and happy, and once that happens, they’ve got their closure, and they’re not terribly invested in other couples in the story to want more in series—they just want more Darcy and Elizabeth in a different incarnation. (If you can think of other sub-genres in romance that are almost all standalones, I’d love to hear—shoot me an email!)
If you’re well-established already: You know your genre, you know your audience, you know how to build a world—you can do what you want. I mean, you can always do what you want, but you have a lot more latitude to do that when you’ve already set expectations really well and readers can count on you to deliver. Kate Clayborn is basically only writing standalones lately, and she comes through with deeply felt emotional highs and lows that her readers expect. E.E. Ottoman has almost always written standalones (I think he has one series?), and you know you're going to get his beautiful prose and delicate care for his characters.
Standalones can always be a springboard to a series, of course, if you end up really falling in love with the characters and the worlds you’ve created in the one-off story you thought was going to stay solo. (Yes, I'm still trying to bring you over to my side of thinking series...)
Series
I think that series are important starting points for most writers, especially early in your career. The first (or second, or third--whichever one they initially pick up!) book has to be the thing that gets readers interested in your work, and then the rest of the series keeps them on the hook and turns them into fans who are invested in your work and continue to seek it out.
Series are also especially good for developing systems in your writing process so that you produce consistently and create a backlist that makes you money. Series also help you build skills you’ll need throughout your career: juggling multiple storylines, telling interconnected stories, finding and sustaining a hook, cultivating a community of fans who are excited about your work, setting expectations for readers and for your own writing/creative processes, etc.
While series are a hell of a lot more work up front, the payoff can be huge. And I’m going to go way more in depth into how series are the key to success and to levelling up your game in my workshop Three Secrets to Becoming an Auto-Buy Romance Author.
We will talk about:
Why we write series (not just because everyone does!)
Implementing strategies in your writing to set you up for success
Building momentum in your writing so you can produce consistently at a pace that works for you
Developing confidence in your abilities to do all of the above
Getting the support you need to write each book in the series