Four years ago I sat down to write the screenplay for my first romantic comedy, Man Up. It was set in London, and was my attempt to look at how romance works in the modern world, and whether you can truly have a blind date anymore. Now that screenplay has been turned into a film, starring Simon Pegg and Lake Bell. Here is what I learnt in the process: my 10 golden rules for how to write a romcom.

1. DON'T BE A SNOB

Romcom is the genre of film that people are most likely to dismiss. But I have always loved them. Long before the term “romcom” turned up in the Oxford English Dictionary in 1971, there were screwball classics such as Bringing Up Baby and Some Like It Hot. Every decade since has reinvented the romcom: Tootsie took a gender-bending approach in the Eighties; Muriel’s Wedding and Sideways focused, respectively, on relationships between two women, and two men; and more recently, Judd Apatow has given the genre his own unique, bromantic twist. The best way to pay homage to something is to make it your own.

Marilyn Monroe and Tony Curtis in Some Like It Hot Credit: Film Stills

2. FIND THE SWEET SPOT

The masterpieces of the genre – Woody Allen’s Annie Hall, Nora Ephron’s When Harry Met Sally, Nancy Meyers’s Something’s Gotta Give – achieve the perfect balance of romance and comedy. If something is making you laugh and cry, you’re watching a romcom (if you’re just crying, it’s probably The Notebook). When that equation works, it’s a beautiful thing to behold.

3. POP THE QUESTION

In Billy Mernit’s essential book Writing the Romantic Comedy (2000), he anatomises the critical elements of the romcom: the chemical equation – what do our two leads need from each other?; the infamous “cute meet” – the unique way we get them together; and the sexy complication turning point. But most importantly, Mernit says that you need to identify a big question, not “Will they or won’t they?” but “What is your film going to be about?” Is it about whether men and women can be friends without the sex part getting in the way (When Harry Met Sally)? Or is it about when to settle, or not settle, in a relationship (Moonstruck)? For me, Man Up is about when the time is right to let down your guard. Neither of my characters is willing to say: “I like you.” There is a constant push and pull between them, which is part of the problem in the dynamic of modern dating.

Cher's Loretta falls for her fiancé's brother (Nicholas Cage) in Moonstruck Credit: The Kobal Collection

4. GET A LIFE

To write about life, love and the pursuit of happiness, you need to live it first. So I got my first job writing for television, and then it took me another 10 years or so – of learning the craft, and finding my voice, and making up and breaking up with boys – before I felt that, at 34, I now had all this stuff to say about life, love and the pursuit of happiness.

Lake Bell plays Nancy in Man Up Credit: GILES KEYTE

There is a tendency for writers to shut themselves away and think they have to go really internal, but I would say the opposite is true – you need to embrace the world to have a mass of inspiration. You don’t have to have killed someone to write a thriller but you do need to have experienced some heartbreak to write a romcom.

5. STAND UNDERNEATH THE CLOCKS AT WATERLOO STATION

The inspiration for Man Up came not long after I’d had my heart broken. A man came up to me at Waterloo Station thinking I was the blind date he was meant to be meeting, and I said I wasn’t… but as he walked away, I thought: “What if I had said I was? And isn’t that a great premise for a movie?” I wanted to write something about two people who had no idea about each other before they met. Internet dating means that you learn about, and reject, people before you meet them. How many people are we dismissing who might have some potential? You see a photo and say No. The Tinder swipe is the death knell of romance.

6. NO MORE MAN-CHILDREN

The Simon Pegg character in Man Up is based on lots of my male friends who are in their 40s yet continue to want to date only younger women. I admire their courage but I also sometimes want to punch them in the face. I wanted my leading man to be like the model Billy Crystal perfected in When Harry Met Sally – hilarious, vulnerable and somewhat quixotic. In Man Up, Jack (Simon Pegg) is reminded by Nancy (Lake Bell) that he is a bit deluded. In real life, this tendency in men may never change, but I thought it was nice to see on screen that a man could face up to that.

7. WOMEN ARE MESSY TOO

I am a big fan of the Diane Keaton-style romantic heroine who is not in control of her emotions. I don’t like female characters who have it all except for a man. In Man Up, Nancy doesn’t just want love, she wants someone who she can connect with and who is therefore probably going to be complicated. I’d like to see messier people on screen, who don’t know exactly what they are doing or what they want.

Diane Keaton in Woody Allen's Annie Hall Credit: Film Stills

8. CHEMISTRY IS EVERYTHING

You can have an amazing script but if your leading man and woman don’t have chemistry, it will fall flat on screen. It probably helps if they like each other in real life. The question I ask myself when I am writing is: “Would you like to hang out with these characters?” If you wouldn’t then you are not going to enjoy the film.

9. THERE'S NO PLACE LIKE HOME

You are trying to create a real world that is believable. My real world, my home, is London and not necessarily the chocolate box version of the city. We did shoot a scene on the Southbank, where 21 years ago Hugh Grant gave his beautiful Partridge Family speech in Four Weddings and a Funeral, but you can see it is a different place now. It was important to me that ours was a rain-soaked, drunken, sweaty London.

10. A ROMCOM IS FOR LIFE, NOT JUST FOR VALENTINE'S DAY

People will continue to meet, fall in love, get heartbroken for all time. As a writer, you should embrace that. And then make ’em laugh, and cry.

Man Up is out on May 29