For instance, if you start to write, you will also start to revise. Which means eying your work with a critical eye for flaws. And if you are prudent, you read other works to see how they do (or fail to do so), in order to improve your own bag of tricks. Do that for long, and you discover you have summoned an imp. He will sit on your shoulder and treat any work of art before him as a sample for analysis. And you can't dismiss him.
I've watched Tangled recently. (Which is a great movie and you should probably watch it before my unsystematic but spoilerific comments.)
While actually watching it, especially for the first time, the imp is particularly interesting in the fine-grained twists that lead the whole story texture and definition and put some skin over the meat that covers the plot skeleton. Which you only need to see the moment to grasp. Still they are skills that are needed. The narration opening, where Flynn solemnly intones that this is the story of how he dies -- quickly changing the tone and adding it's actually a fun story, and not even about him, it's about Rapunzel. The last is a bit hyperbolic, but it introduces him nicely -- as does the scene where he tears down his wanted poster, exclaiming in distress over -- the way it depicts his nose.
Or Mother Gothel's line at the bottom of the tower about not getting any younger. Given that we already know her motives in abducting Rapunzel -- unlike the tale, she has no love for her, but just uses her for magically renewing her youth. It lends it a double meaning. Indeed, just about everything Mother Gothel says has the meaning that Rapunzel will take it in, or would have taken it, earlier, and the meaning the audience can also see in it.
How Rapunzel, stymied in her efforts to show that subduing Flynn shows she's not so helpless after all, manages to change course and persuaded Mother Gothel to go away for three days. (She must have thought very quickly on her feet, then.)
Rapunzel's bracing herself as Flynn goes down the tower, her rapid descent once she gets up the nerve, passing him by, and the final moment where she hangs above the grass, within easy reaching distance, and hesitates, for long moments, before she works up the nerve to commit herself and actually go down. Turning what is happening into the opposite -- a wise thing -- a plot that goes forward too smoothly lacks the texture and picturesqueness to catch the attention.
The mirror that breaks in the tussle between Mother Gothel and Rapunzel. Actually the imp talked of how symbolical appropriate it was, given Rapunzel's refusal to renew her youth again, and so change the looks she saw in it. But then, at the end, of course it was crucial to the plot. Which is the way to plant surprises in the story: give the foreshadowing a reason that fully explains its presence at any earlier point. (Now if only it were so easy to imitate.)
Or when Flynn has called for Rapunzel to let down her hair, started to climb without it, and then it falls -- he's smiling as he climbs, and you know he's thinking that Rapunzel is willing to listen at least, and in spite of the damning evidence against him, he has hope, and we in the audience, who know what's up there, get to watch in anguish. (And we have another twisting of events: from despair to hope to, back up in the tower, more despair. Not quite so elaborate as the montage when they leave the castle, and Rapunzel see-saws between delight in being outside and despair at what a terrible person she was, but that couldn't last all film, being entirely too unsubtle and incapable of all the events.)
Or his perfect line when she revives him. Minimizing the impact of the hair cut in a manner that does not belittle it, and drawing a sharp contrast between him and Mother Gothel, that he loves her for herself alone and not for her yellow hair.
Doesn't even stop inspecting when there is equivalent technique. There are things you can do subtly in fiction but not in film, but draw expressions is not one of them. The way Flynn's face shows what he is thinking and how he is growing you can't really imitiate in fiction. And the royal couple -- Rapunzel's parents are eloquent depicted without a line of dialog between them. Cute moments like Pascal getting a face full of dust as Rapunzel's -- cute moments can be used as local color, but I'm not sure that one would work, since it would probably need more words, relative to the story, than that bit had pictures in the film. Not to mention Pascal's color changes, so seldom in response to his environment, so often to show he's grieved (blue) or embarrassed (red). I've heard he was originally intended as a squirrel, but I can't imagine a squirrel in his place, because they use the colors so expressively and integrally. Then, marrying in your new ideas so indissolubly that no one can tell what is old and what new is part of the art of story-telling.
Some big picture stuff was clear up front. Like the extent of the differences. It wasn't the flower of the sun that set my imp muttering though. It was the discovery of Rapunzel's royal blood. And the scene with the king and queen had him frowning and muttering about the stealing of the rampion. Well, by the time Mother Gothel abducted the princess, it was pretty clear how the parents would be more innocent and the witch more guilty than in the original. But the imp muttered a lot in it. Though, to be sure, there is one definite improvement in terms of unity. When the Brothers Grimm had her tears heal his eyes, there was no hint of foreshadowing of that.
Then, once it's seen once, the imp can thrash about with things -- still more when viewing it a second time, and bearing in mind the last time. Like noting that Mother Gothel's dialog and Flynn's delight on the climb were part of the massive amounts of dramatic irony. Except in the Snuggly Duckling scene, there are no scenes in which we are unaware of the significance of the acts the characters are carrying out, even if they don't -- and even in that scene, it's only the supporting characters, and only at the beginning. And they put its ability to put our emotions through the wringer with consummate skill. We can see the course of events as soon as Flynn walks away from the boat and Rapunzel, and it's heart wrenching.
And one can ponder the character development at leisure and note that while both Rapunzel and Flynn get "boy meets girl" sorts of changes, Rapunzel gets "the little tailor", and Flynn "man learns lesson." A nice exemplum of the types of change, though.