Certain elements are essential for any film, whether it's part of a franchise or not. Every film needs a good editor or it will be bad - editors do not get the credit they deserve. Every film needs a good cinematographer, lighting team, and sound team - if they don't do their job well, it won't matter how great a job anyone else does; the film simply won't work. But in today's film market, the franchise is king and every good movie franchise requires certain elements in order to be sustainable.
1. Source material that can be naturally sustained
A lot of the most popular franchises have been based on book series, meaning that the filmmakers automatically have enough material for multiple films, like Harry Potter, The Hunger Games, and, debatably, Twilight. These franchises can draw on hundreds, perhaps, thousands, of pages of content and thus legitimately make multiple films. Peter Jackson making three films out of the humbly short book The Hobbit is a clear example of the folly of choosing insufficient source material; the films have to be absurdly padded to make feature length running time and thus lack coherence, suspense, and interest. But literary sources are not necessarily the best sources. Though no one could accuse me of being a fan of superheroes in any context, superhero comics are perfectly designed for film franchises. Aside from that large and lucrative fan base, superhero comics have stories that are meant to be sustained episodically and some, I am told, have their characters in split story-lines or time warp situations that make reboots a natural step. Good source material should above all take place in fictional universes, literary or not, that invite reiteration, cultivate interesting characters, and most importantly, provide the basis for multiple story lines.
2. Lots and lots of character actors
My favorite film franchise by far is Pirates of the Caribbean and though I can't easily ascribe my enthusiasm to any one element, if I had to, I would pick the fabulous cast of character actors. Character actors were once a staple of Hollywood filming, appearing in every film regardless of genre, lending variety to the faces, bodies, and voices seen and heard on screen. Character roles tend to be far more entertaining than hero, damsel in distress, or even villain roles because their ultimate destiny isn't defined by their type, nor are their ambitions. Pintel and Ragetti, Murtogg and Mullroy, even Captain Jack Sparrow - these are all character parts and the actors playing them are exceptional character actors. (Johnny Depp is at heart a character actor, but his movie star looks have ironically gotten in the way.) The character actors provide the meat of any good franchise and they are sorely lacking in a film industry that emphasizes youth and misogynistic standards of attractiveness across the board.
3. A distinctive score (by a composer who is not Hans Zimmer)
Not that Hans Zimmer is necessarily a bad composer. His scores, however, exemplify the typical epic, beat-laden music that is usually identified with today's blockbusters; everything sounds like Inception. In just the last four years, Zimmer has provided scores for films from the Superman, Spiderman, Batman, Pirates of the Caribbean, Sherlock, and Kung Fu Panda franchises. The best scores eschew this by now banal style and create a distinctive, unique atmosphere. This is extremely difficult to sustain over a long-running franchise. John Williams wrote evocative and quite beautiful scores for the first three Harry Potter films, each one unique, but linked by common tonalities, themes, and instrumentation. The remaining films were scored by three other composers, with greater or lesser success, but the score became increasingly generic and increasingly Zimmeresque. A distinctive score creates an individual atmosphere, immediately evoking the world of the franchise and sustaining its mystique over multiple films.
4. Quality over quantity of CGI
Though poor quality CGI is a problem throughout the industry, franchise films have a particularly bad track record when it comes to CGI. The emphasis on large-scale spectacle to the detriment of character, plot, and logic has resulted in a serious downturn in quality overall. The solution is simple and benefits everyone. Contrary to popular belief, CGI is neither cheaper nor easier to produce than most traditional effects and film techniques. Case in point - the company that did the effects for Noah bankrupted itself, produced poor work, and received grossly inadequate resources and compensation. Those massive shots of CGI ocean could have been easily achieved with actual footage of the ocean. It would have cost a mere fraction of what was spent on the CGI, could have been handled by a secondary unit, would have taken substantially less time and cost less money, and, most importantly, it would have looked a lot better. It is possible to produce top-notch CGI effects, but CGI should be reserved for things that really and truly cannot be done otherwise. A more sparing use of CGI, and the resources to do the best possible job, are key to producing worthwhile films. Not to mention, I'm pretty sick to death of going to films that look like video games with live actors superimposed onto the footage.
5. Witty, cinematically cultured screenwriter(s)
A well-written screenplay is essential to any good film, but successful film franchises call for a particular type of screenwriter, or more often for these films, screenwriting team. The screenwriters need to have the skill to juggle a large number of characters, keeping them consistent and complex, create logical plots unfolded over multiple films in a way that satisfies the structural demands within each film, and construct a convincing world that viewers will want to explore over the course of many hours. It's also essential that the screenwriters, whether they remain consistently involved in the franchise over time or not, adhere to their own logic. Though I admit I have not managed to sit through more than ten minutes of the Twilight films, I heard frequent complaints that the various supernatural beings had particular powers when the plot called for them and didn't at other logical points. This destroys the fabric of the narrative and it's a particularly difficult issue when plots are spread across multiple films. The best franchises will employ screenwriters that are cinematically cultured (any fan of swashbucklers will find endless homages in Ted Elliot and Terry Rossio's screenplays for Pirates of the Caribbean) and, most importantly, know how to write witty dialogue. Speaking of which...
6. A sense of humor
The trend of making every movie epic, dark, and gritty, has sucked much of the humor out of many a franchise, but it's an essential element. The tediousness of the later Harry Potter films can be largely attributed to their deadly seriousness (in contrast to the novels, which even at the most dramatic moments retain an irreverent sense of humor), while many other franchises begin to seem like parodies of themselves (not to keep ragging on Twilight, but it's the prime example). Once again, Pirates of the Caribbean gets full marks - they're consistently witty and funny - as do the Scream films and the original Star Wars trilogy (though I may be laughing at the latter, rather than with it). Humorlessness gets old very quickly, and the more epic the story, the sooner it begins to seem utterly ridiculous. A judicious dose of humor is essential for the sustainability of any film franchise.
7. A committed cast and production team
And I mean committed in a variety of senses. Hopefully, the people making the film should be enthusiastic about it, but more importantly for a film franchise, they have to be willing to commit their time for the long-haul. Few things are as disruptive to a film franchise as a major player dropping out. Imagine if Johnny Depp left the Pirates of the Caribbean franchise or if Daniel Radcliffe had bowed out of Harry Potter. Even worse, and far more common, than replaced cast members are replaced directors. Switching up directors hit the Harry Potter franchise hard, resulting in a series that is frequently incoherent, with each director's contribution tugging the series in a different direction. Such changes have less impact when the films are not meant to tell a continuous story (which is the case for many superhero franchises), but the strongest franchises hold onto their significant players.
And, bibbity bobbity boo, a great film franchise. Get these seven ducks in a row and you're set. It seems like I'm missing something though...
Oh, yes. A great deal of money.