Two Stephen King big-screen adaptations, released a month apart, had disparate fates at the box office. We examine why “It” proved to be a monster hit while “The Dark Tower” collapsed.

Embrace the R rating

Although they’re considered fantasy novels, King’s “Dark Tower” books are loaded with bloody violence, sex, and adult language. And yet “The Dark Tower” film went out of its way to trim the material to get a PG-13 rating, presumably so that it would appeal to a much wider audience than it would if it was rated R. That clearly didn’t work. “It,” however, stuck to its guns and went for the solid R rating, and the result is obvious. The lesson being? If the material on the page is inherently R-rated, then the movie adaptation should be, too.

Stick to what’s on the page

Although “It” changes several small details and eliminates some unnecessary subplots, it’s a very faithful adaptation of the first half of King’s novel. The structure is virtually identical, and many of the sequences are lifted wholesale from the book. That’s not the case at all with “The Dark Tower,” which functions in some ways as a prequel to the book series. While it contains echoes of specific images and scenes from a few of the books, it’s basically an entirely original story that happens to take place in the series’ universe. The lesson? If you buy the rights to a King novel, adapt the actual novel. He’s already worked it all out for you.

Make one movie at a time

Before it had even opened, the producers of “The Dark Tower” went out of their way to detail their plans to expand the story’s universe beyond the first film. A television version was promised, with the idea being that it would serve to bridge future movies, tying the whole thing together like Marvel’s superhero film series. In hindsight, it’s clear that they put the cart before the horse. The makers of “It” corrected that mistake by concentrating all of their efforts on making and selling a single movie, even though it was obvious that there was a second half of the novel still to come. The lesson? Selling audiences on a franchise when they haven’t even seen the first movie risks alienating people and scaring off potential viewers.

Pick an image that moves people

Despite all the trailers and marketing, “The Dark Tower” never found a specific image on which to sell their film. The final poster was a colorless cityscape with the outline of a tower hidden inside it. It looked less like an imaginative action-fantasy and more like a movie about real estate and architecture. The dull character posters featuring Idris Elba and Matthew McConaughey weren’t much better. “It,” on the other hand, landed on the perfect image to sell a horror film. The poster’s bright red balloon became an instant shorthand for terror. The young boy’s memorable yellow raincoat stands out graphically, and the ghostly image of Pennywise the Clown is all audiences needed to see. The lesson? When you’re making a King movie, pick an image that will worm its way deep beneath viewers’ skins, and stick with it.

Stephen King is the real star

“The Dark Tower” features two major movie stars in the lead roles, but “It” has an entire cast of newcomers. So why didn’t audiences for “It” mind seeing fresh faces on screen? It’s because King himself is the film’s big star. Although King didn’t have much direct involvement in either movie, “It” clearly embraced his name in virtually all of their promotional materials. “It” is a property that’s instantly identifiable as a King story, even by those who’ve never read it. “The Dark Tower,” on the other hand, often surprises people when they hear it’s based on a series of King novels. Perhaps the producers of “The Dark Tower” should have spent less time worrying about whether or not Elba could play the gunslinger, and concentrated more on developing the King connection.