"Well. That escalated quickly."
Have you ever been reading a book or watching a movie and suddenly think the plot jumped waaaaay ahead of the timing? Here's a common one I run into in my genre: two characters meet, discover they dislike and sometimes even hate each other, and on the next page they've never felt such incredible magnetism, never been so drawn to another. On the next page, they're inexplicably in love.
There's the kicker: it's inexplicable. The characters have had no time or experience to bring about this change of heart: they are simply overtaken by mysterious, unexplained love.
Alright, let me be straight about something: I love Willow, and I love the Madmartigan/Sorscha pairing. And of course, they got a little help from some fairy love dust. They do make a good example of the love/hate dynamic, though, don't they?
In romance especially, pacing can be tricky. Clearly you want your characters conflicted because you want them to grow closer through overcoming obstacles. But you also want to get to the good stuff. And, of course, you want them to have their happy ending. So I find, in a lot of romance, characters surmount all odds and find their true loves... suspiciously quickly.
For me, that's a story worthy of a good side-eye, and I lament the story that could have been, if only the writer had let it "go through its paces".
If you're a writer looking for ways to build a good pace in your romance, here are a couple of tips:
Use "Chekov's Gun". Go ahead. It's okay.
I recently read some criticism of JK Rowling using deus ex machina in Harry Potter, but I think she used the much more effective Chekov's Gun: "an insignificant object that later turns out to be important" (according to TV Tropes). Rowling tends to introduce either literal objects or magical lessons and concepts early in her books, and they become more significant than expected later. We see Ron's interest in Wizard Chess early in The Philosopher's Stone; at the time it doesn't seem significant. There is a reason Rowling shows us, though: later on, Ron's skill comes into play in an exceptionally significant manner.
Consider this: let's say we never saw that earlier, seemingly unimportant scene of two boys killing time with a game. Then, at the end of book, suddenly we discover Ron just happens to be great at Wizard's Chess, which allows them to bypass a dangerous trap. In this case, we would cry Deus ex Machina. We'd be asked to accept a coincidental golden key happens to be exactly where Harry needs it at exactly the right time.
By giving us a glimpse at the key earlier on, without necessarily telling us that's what she's doing, letting us absorb the knowledge as a natural part of the story, Rowling sets the stage with an 'establishing shot'. This eliminates the feeling of "coincidence"; Ron's role in the final victory is not inexplicable.
It should be noted that foreshadowing doesn't necessarily require a 'gun'—or any object at all. My example used a person's skill, and the concept of a children's game. The effectiveness of Chekov's Gun lies in you laying the groundwork for important developments later on.
Give your readers a breather.
I'm going to admit something here: I hate The Dark Knight. Honestly, the movie is one big headache to me. I have a reason, though: there isn't any down time. The movie is all rising action, no space to breathe.
Agree or disagree with me on the movie, but my point is this: when you introduce conflict, you need to balance it out with time to absorb that conflict. When you go straight from drama to drama, you rob the characters and readers of the chance to absorb and reflect.
Pepper your action with time to decompress. Let the characters reflect on what has happened—this gives you the chance to establish all those things like shifting emotions or ideas that solve the mystery. This way, when your heroine starts wondering where her sudden feelings of passionate desire came from, they're not so sudden.
Sometimes I think writers—myself included—get 'bored' with these 'downtime' scenes. Perhaps we feel the urge to avoid them because we feel they will bore our readers. Consider this: what do your favorite authors do between scenes of high action? They use scenes of discussion, reflection, low-action. Has this ever bored you into putting down their books?
Consider your Believability
Go back to my very first example: the couple who hates each other in one chapter and become true loves the next. What's the biggest problem with this? It's not believable.
This is what makes me roll my eyes the most. There's suspension of belief, and then there's flat out cheating.
Anything is possible, but there have to be reasons that it happens. Your reader needs to be able to believe it happens. This means actions must have consequences, and consequences must be dealt with. You must eliminate excessive 'coincidences' and 'lucky breaks'. This will, of course, require time out of the story, but that's where you balance your action in pacing. It also heightens the stakes and makes the growth of characters more appreciable.
So when you write your conflict, consider the believable consequences of your character's actions. Reflect them—even if it's hard. If it's too hard, it's possible you've chosen too big a conflict. Don't be afraid to rethink it—but don't cheat by helping your characters out with an unbelievable stroke of luck.
Pace your stories. Give your conflict consequences. Make your characters own their actions and earn their happy endings.
And enjoy the full, developed and rewarding story you give yourself as a result!