The success of a book rests upon its characters. Are they interesting? Great. But… What do they do during the course of your book?
They could skip about and yak and tra-la, but most readers would find that dreadfully boring. So your characters must act toward a purpose. They must have a goal.
Say your heroine wants to save the house she grew up in, slated for demolition. That’s faboo! This is what we call an EXTERNAL goal, something that the character wants outside of themselves. But the more meaningful goal is usually the INTERNAL one. Sally wants to save the house because she was mean to her mother before she died, and her mother always loved that house. Saving it is a way to soothe her guilt about how she treated her mother.
But wait! The current owners are behind in payments to the bank and the people there want their money. They aren’t going to sell to Sally but rather to the developer who wants the house merely for the land it’s on so he can build a brothel that also stocks illegal drugs which they plan to sell to the kids in the kindergarten next door. The bank and developer are now the ANTAGONISTs, the entities that push against the efforts of the PROTAGONIST (Sally) in order to try to stop her from achieving her goal.
If you’ve structured things really well, the Protagonist and Antagonist’s quests to fulfill their different goals will make them run smack up against each other time and again. Drama! Things are going to get worse and worse and worse for poor Sally until she figures a way to best that nasty ol’ bank and get her house… If that’s what she really wants by the last chapter of the book. Goals often change over time.
There are four major turning points in a book: the first, just a little ways into the beginning, is the "invitation to adventure," where a problem first appears and your protagonist has to make the decision to DO something. At the end of your first act, once everything is proceeding apace and you're about a quarter of the way in, you have another turning point into the second act. Then there’s one at the midpoint, which is at the middle of your book and the second act. This is a biggie, with something good usually happening to Our Hero/ine, but right afterward everything reverses into giant uh oh! Then there’s another turning point at the end of the second act, which is about 3/4 of the way through. (After that comes your third act which will be the concluding one.)
The great Jenny Crusie says that at every turning point you have to ask: “What does my character want?” At the turning point after that, you have to ask, “No, what does my character REALLY want?” and so on. See? You’re peeling back onion layers of personality, as Shrek's Donkey would say.
As we get deeper and deeper discovering Sally’s internal goals, we might find her external goal changing as well. She wants to save the house. Then she wants to save something inside the house. Then she just wants to save some precious keepsake of her mother’s that’s been left inside. (By now she doesn’t want to assuage her guilt; rather, she wants to show her mother’s spirit that she loves her.) Maybe something might spur her to create a huge campaign that will save not only the entire house, but the neighborhood as well.
Or not. The final goal doesn’t have to be big but it does have to be DEEP. There should be some kind of progression with at least a slight changing of goals that mirrors how your character changes from the start to the end of the book. (The character arc.) As your character learns about life and how to handle it in different ways, their view toward their internal and external goals will change.
What, your character doesn’t change? Hm. Are you sure you have a solid story? If you do, something’s changing. Look again. Is there someone who changes a lot during the course of your story who isn't your current Hero? Maybe they're the real protagonist. (I've used the wrong protagonist twice in my proto-novels. It's not that big a deal to focus in on them instead of your previous Hero as things begin to fit EVER so much better!) Exaggerate the change if you must. I think you’ll be pleased with the result. You want drama! You don't want just to grab your reader; you want to grab and SHAKE them!
If you’re writing a romance you’ve got both Hero and Heroine. They will PROBABLY (not always) be acting as antagonist to the other while they’re their own protagonist, and their quest for their individual goals will clash terribly. Perhaps there’ll be another antagonist, worse than either of them individually, so that the H/H will have to combine forces to overcome the problem the Big Bad brings.
That’s how conflict works for the entire book. Now look at your individual scenes. Each scene is going to have conflict within it as well. It’s a book in miniature. If you can’t find the conflict in your scene, maybe you can live without it.
Don’t get scenes mixed up with “sequels.” A scene is a unit of your book in which action takes place. The result of it is NEVER EVER a “whew! I got it all done!” (“yes”) unless you are on the final chapter of your book. A scene will always end with some kind of disaster. If you read Scene & Structure, by Jack M. Bickham (and you should!), you’ll discover that your protagonist will try to accomplish their goal despite an antagonist (who doesn't have to be the book's antagonist, but rather the antagonist only for that scene) during a scene. They can wind up getting a “yes, but” conclusion with some kind of condition applied to obtaining the goal. OR, amping that up is a “no, but” which gives the protagonist some small hope of getting that goal. Then there’s “no, and further more,” which is a hard slap that sets them farther back from their goal than they were to begin with. Cool!
A “sequel” in this sense is not Star Wars V but rather a unit of fiction-telling in which the protagonist has to emotionally react to what they’ve just been through in the preceding scene (that slap-down!) and then make plans for what they’re going to do in their next scene. Sequels can be long pages of planning and angsting, or they can be one line long. Or even glossed over and revealed in a line or two or suggestion in the next scene that shows the reader that our protagonist planned whatever it is they’re doing now. That’s why Sally has put on a man’s suit and fake beard and has just entered the bank; the sequel is now implied within the scene that she's planned a masquerade for some purpose.
So you should have conflict at every level in your novel. Otherwise, it’s just a tea party with people congratulating themselves about how wonderful they are.
I have a saying posted on the bulletin board behind me: “In fiction, the best times for the writer—and the reader—are when the story’s main character is in the worst trouble." Don’t coddle your characters! I know you love ‘em to pieces. But if you really love them, you’ll cause them trouble. Big ol’ handfuls of nasty-wasty Trouble!