Boy Meets Girl. Boy and girl spark off each other. After ninety minutes or so, they decide that they're in love and belong together; unfortunately, fates have usually conspired to keep them apart. Will they find each other again and live Happily Ever After? Have a guess. The romantic comedy genre is one of the most popular film genres out there; count how many films are released in a year, and see how many of them follow the rough template established above. Audiences love to watch two people fall in love and find their happily ever after, usually with each other. However, Sturgeon's Law applies, and a lot of those comedies are terrible. Do not despair if you're thinking of writing one, however; the good people at TV Tropes Wiki have sat through many of these and identified what works and what doesn't, and how this might hopefully help your effort be the best it can be. Of course, be sure to check out So You Want To Write A Story for basic advice that holds across all genres. We also have So You Want To: Write A Love Story? for slightly more detailed, if still generalized, ideas about romance.
Necessary TropesWell, first you'll need a Protagonist and a Love Interest (although if you wish to try for a Romantic Comedy about onanism, by all means). You can decide which will be the man and which will be the woman (or vice versa, or both). You will also need a Beta Couple to underscore the romantic tribulations of the main two characters; generally these characters are the Protagonist and Love Interest's Best Friends / Direct Siblings / Both and act as advisors and comic relief to the main couple and the audience. They may or may not get together at the end; alternately, they may be used to provide a counterpoint to the main couple (i.e. if the Protagonist is lonely and love-lorn, his / her counterpart in the Beta Couple may be happily married with kids). Check out any of the tropes in the Romance Arc; most, if not all, will be essential in a romantic comedy. In particular, 'comedy' these days generally implies 'Happily Ever After', and audiences will probably feel cheated if the characters don't end up happy, or at least content, at the end. Check out the Love Tropes as well. Generally speaking, most Romantic Comedies tend to involve Opposites Attract - watching two people who apparently have nothing in common is often more interesting so see if they'll overcome their differences to get together (and more satisfying when they do). There's a lot more tension involved as well; audiences for these movies like to see a bit of Slap-Slap-Kiss before they get together (not literally, of course; aside from the unfortunate connotations, the actual Slap! Slap! Kiss! scene is a bit of a Dead Horse Trope these days). Whether the Protagonist and the Love Interest are friends or enemies initially, there will also be some Unresolved Sexual Tension between the two; it's the chemistry that draws people in to watch and see whether they get together. If they don't possess this throughout but get together anyway, the audience will most likely find it a bit unsatisfying. At the end, there will usually be some kind of Race for Your Love situation, where the Protagonist desperately has to chase after the person they love before they walk out of his / her life forever. There may also be a Concert Climax situation where a very public declaration of love is made, followed (hopefully) by a Concert Kiss. Oh, and, it's a comedy, so you need to be funny. If you lack this talent, do not attempt to write a romantic comedy.
Choices, ChoicesFirstly, who are your two love birds? What backgrounds do they come from? How are they different? How are they similar? Are they Birds of a Feather or will Opposites Attract? How does their relationship progress? Is it Love at First Sight or do they hate each other with a passion? Are they two strangers who find themselves bumping into each other in a Meet Cute situation or are they two old friends / or enemies — who find their Like Brother and Sister or tense relationship becoming something very different? What kind of tone do you want to establish? What kind of jokes do you want to tell? RomComs are typically light-hearted affairs which emphasize the idea that Loves Makes You Dumb and can lead you into all manner of silly, embarrassing situations. However, there is also a trend of deconstruction where the "Love Makes You Dumb" trope is Played for Drama instead. The resulting laughs are more in the vein of Black Comedy. While this is a bleaker tone to manage, it has the added benefit of being a lot more realistic: while a sizeable amount of the world population has experience in successful long-term relationships, a much larger demographic, approaching 100%, has experience with failed ones. Finally, because one of the (typical) goals of dating is to find someone to have sex with, RomCom has the option to multi-class into Sex Comedy, which is always a wellspring of amusement.
PitfallsWhen it comes to pitfalls, this genre is a minefield. Fortunately, so many others have been through it before you (and blown themselves up) that there's plenty of signs to show you where you might be misstepping. As the Romantic Comedy is a very common, very popular genre, it's easy to get lazy with it. Unfortunately, the audience will be able to tell if you're just going through the motions. It's also very formulaic in many ways, and can be quite predictable for much the same reasons; try and think of different spins you can place on the situation, or subversions of obvious tropes that you can make (some suggested below). Specifically, it's also very easy for reasons to keep the lovers apart until the very end to come across as being contrived or unconvincing; if the plot is demanding that the lovers be kept apart, then the reasons for this should be natural and logical, and should stem from the characters themselves rather than outside contrivances. It's also common to set up a Love Triangle situation with the Protagonist, the Love Interest and Romantic False Lead, someone whom the Protagonist must compete with in order to win the Love Interest. Be careful with this character, because they often operate more as a plot device (they're essentially a tool to keep the characters apart) than a character in their own right. Making a Romantic False Lead can be difficult to pull off. Making him/her too much of a Jerk Ass (or a bland, boring non-entity) will result in the audience wondering why the Love Interest is with the Romantic False Lead sees and, consequently, whether the Love Interest is even worth persuing (since he/she obviously has poor taste in romantic partners). On the other hand, making the Romantic False Lead too much of a nice guy will result in the Protagonist coming across like a selfish Jerk Ass for trying to destroy a healthy relationship. Furthermore, having a Romantic False Lead seem like a nice guy but suddenly reveal themselves to be a jackass can come across as inconsistent (and unbelievable). There is a middle ground, however, wherein Romantic False Lead is a convincing romantic rival but also has enough flaws to justify being rejected. This middle ground can be quite tricky to find though. Be wary also of setting up a Runaway Bride situation as well, where the Love Interest dumps Romantic False Lead at the altar to be with their true love; unless you really play it well, this might seem less an affirmation of The Power of Love, and more an illustration of the Love Interest as Heartless Bitch (or, less frequently, Heartless Bastard) - s/he couldn't have let their future spouse down in a less publicly humiliating and destructive fashion? Try not to make it look as if you are merely Cleaning Up Romantic Loose Ends when protagonist and Love Interest eventually get together. They should come together naturally, not forced together simply because the writer insists. Avoid, avoid, avoid the Three Is Company trope wherever possible; the old 'the characters are kept apart by a half-cocked reaction to a misunderstanding that would be easily resolved if they just actually slowed down and spoke to each other about it for a minute' device is not only painfully contrived, it's also cliched and hackneyed, and tends to rely heavily on the Idiot Ball to prevent the characters from actually talking through the misunderstanding. Same with the Poor Communication Kills tropes in general, really. No Sympathy can also be grating and annoying for the audience; if the character has obviously gone through hell and back for the sake of their loved one, then if the loved one merely spits in their face despite all evidence to the contrary, it tends not to reflect well on them. Both can be used, however; but after being used poorly for so long, it's really very difficult to pull them off well. Romantic comedies are, in general, a very upbeat, optimistic genre; this can, however, tip over into Sickeningly Sweet or even Tastes Like Diabetes if you're not careful, which is guaranteed to lead to both copious amounts of vomit and your work showing up on the Narm index very swiftly. Avoid Sickeningly Sweethearts (being in love is wonderful, but doesn't mean you have to get ridiculous about showing it), and be wary of the Romantic Plot Tumor. Rousseau may have been right, but that doesn't mean you have to get crazy with it.
Potential SubversionsThere's tremendous symbolism in the fictional union of Man and Woman, or so claims Christopher Booker. By putting the focus on the love itself on a backdrop of any other plot, the Romance genre distills the symbolism to its essence, showing us two characters who overcome both internal and external obstacles to ultimately come together in the bonds of True Love. Some might even say that it's the job of the Romance genre to be at least that predictable. So messing with the basics can make for a less satisfying work... maybe even a flawed work (go read Booker's The Seven Basic Plots for more info on this). Still, there are possible ways to subvert the traditional elements of the Romance:
Suggested Themes and AesopsLove Wins, basically; regardless of the odds and difficulties it brings to the characters, Romantic Comedies nearly all assert that Love is ultimately worth it; it enriches our lives, connects us with other people, and brings us happiness and fulfillment. Even if you choose to have a subversion and not have your characters get together, at the end of the day you'll still want to keep this in mind and suggest that Love is still worth it, that they aren't broken and will try again; Romantic Comedies that end on a note of bitterness and misery rarely succeed or are well received. Love might hurt, but whilst you may wish to indicate this you shouldn't overly-dwell on it. Also, in some ways Rousseau Was Right; most people, regardless of their character flaws, are inherently decent, caring, capable of giving love and worthy of receiving it in return. Love Redeems us all in the end.
Potential MotifsChristopher Booker invests a lot of symbolism in his idea of The Comedy, which to him means a pair of lovers kept apart by either (1) the Antagonist or (2) the Hero, while the rest of the cast suffer from general confusion and misunderstanding that keeps them from getting into the proper and fulfilling relationships they're destined to enjoy. Once the Hero or Antagonist comes around (Booker claims it's usually a Heel-Face Turn that ends a comedy, though occasionally the Antagonist is driven off rather than redeemed), everything is brought to light, everybody finds their proper mate, and there's just a general rejoicing, as though a blight has been driven off the land. So if you want to invest your story with symbolic roles and relationships, and especially if you want to rise to the level of Shakespeare with three or more couples who through misunderstanding and confusion can't get together until the end, then set yourself down for a long read with Booker's The Seven Basic Plots. (Long, long, long read. But it's good stuff.)
Suggested PlotsThe Romance Arc, essentially.
Set Designer / Location ScoutThere's a great deal of possible variety here - the great thing about love stories is that they can happen to anyone anywhere anywhen, so there's great potential. For reasons of cost and ease, however, many of them are set in the present in a major city (New York and London are popular candidates).
Props DepartmentNot a great deal needed here - all you really need for this genre is a camera and two people, minimum - but you can always work something in. The big climactic get-together scene is usually good for this sort of thing.
Costume DesignerAs above, the variety of settings influences the variety of possible costuming available; you may wish to use costuming to give the audience a sense of character.
Casting DirectorYour Love Interest should be charismatic, engaging, and charming, but your Protagonist should be a lovable loser with whom your target audience can identify. By doing this, your target audience can see themselves getting the charismatic, engaging, and charming Love Interest that the lovable loser gets in the film. The lovable loser Protagonist can be of either gender (for examples... in "Along Came Polly" it's the guy while in "My Big Fat Greek Wedding" it's the girl). We should like both the lovable loser Protagonist and the awesome Love Interest, because then we will also want them to ultimately find happiness with each other. This doesn't mean they have to be (or even should be) perfect exemplars of human perfection, however; they should also possess character flaws and issues which affect how they engage with each other and how their relationship develops with each other. It'll be much more interesting for audiences to watch / read two flawed but ultimately decent people overcome their faults in pursuit of love than to watch two paragons fall for each other and become the Perfect Couple; that way, you'll also avoid Sickeningly Sweethearts. Your Alpha Couple also needs that oft-mentioned, ill-defined quality of 'chemistry' with each other; they need to spark with each other. This creates Unresolved Sexual Tension with each other that keeps the audience watching and guessing, and also makes the relationship credible. This is difficult enough on paper, but is super-hard if you're casting with actors, because chemistry in live action isn't just something that happens in the dialogue; it comes from the actors and how they play off each other. If the main couple really dislike each other off-screen and are incapable of hiding it, it'll show in the final product; obviously you can't make people like each other, but you'll want to make sure they can at least hide their dislike as much as possible.
Stunt DepartmentVery few opportunities, it must be said, unless you're combining your Rom Com with another genre. The Race for Your Love sequence may offer a few possibilities, however.
The Epic Fails40 Days and 40 Nights had outstanding examples of Three Is Company and No Sympathy. Seriously Dude, Not Funny!!