Extended universes are all the rage in Hollywood these days. Following the success of the Marvel Cinematic Universe—which reached a record-breaking milestone with Avengers: Infinity War, a crossover event years in the making—studios are trying to piggyback off of the trend with their own prospective franchises. The ones who have so far have mostly struggled (apologies to the DC Extended Universe and Universal’s “Dark Universe”) but even so, the craze isn’t slowing down. We’re not that far away from King Kong and Godzilla once again sharing the big screen.

But while the cinematic universe is a more recent trend in moviemaking, the same methods have been embedded in television for decades—going as far back as The Mary Tyler Moore Show’s multiple spinoffs in the 1970s and the Cheers television universe that existed in the late ’80s and early ’90s. Currently, you can find plenty of TV extended universes in the growing glut of Peak TV, from Christine Baranski’s F-bombs on The Good Wife spinoff The Good Fight, to the many different versions of NCIS, to Dick Wolf’s Chicago shows. And it won’t be long until these series are joined by even more universes, like the one Freeform is building around Pretty Little Liars, the budding Star Wars TV universe, and HBO’s expansion of the world of Game of Thrones. This isn’t a fad with an expiration date; it’s an ongoing enterprise.

However, not all TV worlds are created equal (no offense, Chicago [Insert Random Profession]). There are dos and don’ts when it comes to crafting a small screen universe, lessons to be heeded. As the next crop of extended universes approaches the television landscape, here are four ways to ensure that the final product works, along with one crucial mistake that should be avoided.

Play With Different Genres, If Possible

This is trickier for some shows than others. For instance, the same legal discourse and operatic twists of The Good Wife are essential to The Good Fight. In that universe, the audience is looking for courtroom drama and nothing else. But for extended universes that have some wiggle room, genre experimentation allows shows to stand on their own feet and play with different tropes than the series that laid the foundation.

Take the Netflix-Marvel universe, composed of Daredevil, Jessica Jones, Luke Cage, The Punisher, and Iron Fist, plus the crossover miniseries The Defenders. All of those series take place in New York City and operate under the same umbrella—and sometimes, the characters cross over series lines—but they’ve embraced surprisingly varied tones. Jessica Jones is a superpowered spin on a neo-noir detective story; as a wannabe John Wick, Daredevil is always looking for its next epic action showcase; The Punisher is a gritty, bloody, hard-R treatise on war-induced post-traumatic stress disorder.

Not all of the Netflix-Marvel shows have worked—the less said about Iron Fist, the better—and they still all adhere to a specific set of tropes, but there is enough variation in their offerings to appease a larger portion of TV watchers. If Jessica Jones’ neo-noir vibe is not your style, perhaps Luke Cage’s cheeky nods to its blaxploitation roots is, and so on. The Netflix-Marvel universe is far from perfect, but its strength lies in its versatility.

In a similar vein, Ryan Murphy’s American Horror Story anthology series has tinkered with multiple horror subgenres over its seven seasons—from the relatively straightforward haunted house thrills of the first season to the paranoid, Trumpian overtones of its latest season. (While it’s not official, the show has been teasing for years that all American Horror Story seasons are connected within the same universe.) The megaproducer’s greatest hit is going on eight seasons for a reason: While you know generally what to expect, you never know exactly where each new installment is headed.

As TV universes continue to expand with more spinoffs—the CW’s Arrowverse will have seven different entries by the end of 2018—it’s important that these small-screen worlds offer contrasting genres, rather than the same flavor each time.

Don’t Fear the Prequel

Prequels don’t always work. In their worst manifestations, they reaffirm what you already knew about a certain character or moment in time. They’re also a treacherously tricky creative enterprise, because when you know how particular narrative threads will end—because you’ve already seen the future—tension needs to be derived from something other than the element of unpredictability. But not all TV prequels have been a disaster; there are a few shows that have proved that they can enhance the overall value of a TV universe.

AMC’s Breaking Bad spinoff, Better Call Saul, takes place before Walter White ever becomes Heisenberg; in fact, White’s not even a character, just a looming matter of fact. The show instead focuses on the transformation of straightlaced Jimmy McGill into the slimy Saul Goodman we know and were repulsed by. (I never realized Saul Goodman phonetically works as “S’all good, man!” until the show pointed it out, and I’m ashamed of myself.) The stakes are far less dramatic than Breaking Bad’s—unless you consider the minutiae of elder care law high-octane—but the character development is nuanced and informative. Jimmy’s antagonistic relationship with his older brother, Chuck, has sowed the seeds for the former’s evolution into Albuquerque’s sleaziest legal counsel, in a manner that not only justifies why Breaking Bad’s Saul Goodman always felt like a caricature of himself, but also empathizes with him.

We may know the road ahead for Saul in Breaking Bad, but Better Call Saul has made viewers invested in the journey toward that destination. If a TV universe can justify combing through the past to enrich its previously introduced characters, it’s more likely to have a promising future.

Impending TV universe extensions can take valuable lessons from Better Call Saul’s world-building and enact them on a grander scale. If the word of George R.R. Martin himself is to be taken at face value—and maybe it isn’t, because when’s that next book coming out?—the upcoming Game of Thrones spinoffs will all be prequels of sorts. They may not touch on stories like Robert’s Rebellion that directly involve characters from the original series, but they will all reference mythology that most Thrones obsessives are familiar with. It’ll be imperative then that these spinoffs follow Better Call Saul’s lead by subverting audience expectations and toying with preconceived notions. The stories HBO chooses to tell in the GoT universe should expand our view of the world, rather than merely serving as high-budget retellings of previously established lore.

Introduce New Characters Who Hold Their Own Weight

An expanding TV universe needs to bolster its roster for more projects: It’s great that Better Call Saul was able to center around an established character in Saul Goodman and bring back Gus Fring and Mike Ehrmantraut, but the show works because it gives Saul a new foil in Chuck, and a compelling best friend–love interest in Kim Wexler. It’s not just Breaking Bad’s greatest hits.

Perhaps the best example of a TV universe expansion successfully incorporating new characters is a show that millennials like me may not even realize is part of a TV universe. I spent years assuming Frasier was its own thing, when it’s the most successful spinoff of Cheers. And for good reason: It introduced the world to Frasier’s equally neurotic psychiatrist brother, Niles.

Niles has been described by actor David Hyde Pierce as what would’ve happened to his brother if he didn’t have his Boston bar hangouts from Cheers. He’s somehow more snobby and standoffish than Frasier, often serving as his main rival for their petty disputes. Most importantly, Niles is hilarious; his acerbic wit is equally gut-busting as Pierce’s physical comedy.

Frasier doesn’t work without Niles and the rest of the show’s new faces. Frasier Crane is merely the building block on which Cheers widened its scope, and all other TV universes ought to follow the same model. When Jon Favreau’s live-action Star Wars rears its head on Disney’s new streaming service, fans should become invested in new characters and follow their story, rather than returning to the Skywalker soap opera that’s long worn out its welcome. Recognizable characters can push the envelope only so far. (To Favreau’s credit, he says he’s looking to explore a time period that doesn’t overlap with any of the films.)

Familiar Faces Work—With the Right Execution

That said, it’s the established characters from the start of a TV universe who can entice fans of an original series to stick around; wiping the slate completely has the adverse effect of losing an established audience. Take Angel, the Buffy the Vampire Slayer spinoff that expanded the Buffyverse.

Angel (David Boreanaz) was a natural candidate to branch out from Buffy: He was a fan favorite—the kind of objectively hot, mopey character that’d set Peak Tumblr ablaze—whose utility had run its course in the original series after three seasons. (Sorry Buffy-Angel heads, but the show remained interesting when it let Buffy have her own agency that wasn’t tied to vampire boyfriends with lost souls.) (Honestly, all of Buffy’s boyfriends were pathetic.)

With Angel, fans of Buffy—and perhaps even viewers who missed out on Buffy and figured the spinoff might be worth a shot—had a new show with recognizable faces (original Buffy characters Cordelia and Spike were also series mainstays). But most importantly, and despite the built-in familiarity, Angel wasn’t just a like-for-like remake of Buffy: Angel was an antihero seeking redemption while battling his personal demons, a monster fighting other monsters as a rogue detective.

As with every other quality of a good TV universe, it comes down to execution. Angel unquestionably existed in the Buffyverse, but it would never be mistaken for the original show. The character acted as a tether to a safe, comfortable place, while exploring new, uncomfortable territory. Just because two shows exist in the same universe and feature some of the same characters, does not mean they have to have the same narrative and thematic beats. Unfortunately, that issue plagues the worst kinds of TV universes.

Avoid: THE EXACT SAME THING

This sounds very obvious and avoidable, but television is cluttered with shared universes that serve as a creative copy-paste, with shows that have analogous scenarios and tonal repetition. The Walking Dead spinoff, Fear the Walking Dead, presented yet another postapocalyptic group jumping among different communities that inevitably fall apart before they move on to the next juncture; the short-lived A&E drama Breakout Kings was Prison Break, except the fugitives were helping catch other fugitives (???); and the CSIs, NCIS, and Law & Orders of the world are procedurals whose most groundbreaking alterations are a change in metropolises.

Breaking out of a creatively draining ouroboros is crucial to a shared universe’s success. The Walking Dead and Fear only just came to this realization, making a hard reset that transferred a longtime Walking Dead character to Fear and turned the latter into a Mad Max–esque apocalypse full of SWAT vehicles (a great idea).

Breaking out of the familiar tropes of a shared universe doesn’t always work—Law & Order’s attempt at a true crime anthology series never caught on—but if a TV universe is going to stand out in Peak TV, divergence from the status quo is vital.

While there’s no one formula for making a good TV universe—Better Call Saul couldn’t be more different from Frasier or the Netflix-Marvel enterprise—the ingredients for sticking the landing are often a careful mix of new themes and characters, along with clever callbacks to a small-screen universe’s original material.

Like the MCU, the extended TV universe in its many forms has shown no sign of slowing down. Just one day ago, Epix announced a series centered on Batman’s freaking butler. Television may be becoming even more reliant on preexisting intellectual property—but that doesn’t mean it necessarily has to grow stale.