It's writing post time, and this topic is taken from something I'm currently dealing with: how do you fix a scene that's just not working?
Unless you're a total genius (or entirely oblivious), you probably recognize the problem, either in a first draft or in editing. You just can't get a scene off the ground. It lies there, limp and lifeless. There's no momentum moving forward in the story. This may even be where writer's block sets in -- you can't make that scene happen, which means you can't move on.
Here are some things you can consider to get out of the bad scene doldrums:
Think about the scene's role in your story. Why does this scene need to be in the book? A scene needs to reveal a critical piece of information, reveal something important about the characters, change the status quo, and/or move the plot forward. Preferably more than one of these things. A scene that's just there to explore a cool setting or to make something interesting happen that isn't required to the plot is probably never going to work. Ask yourself how it would affect your overall story if you deleted this scene. If you can delete it, do so. If it only does one thing or if it involves an interesting event, maybe you could combine it with another scene and use the interesting event to further the plot.
The scene's protagonist/viewpoint character must have a goal. What does the viewpoint character want to achieve in this scene? This may or may not be the story goal, but it should probably be at least somewhat related to the story goal. It may be a minor subset of the story goal. For instance, in a mystery the detective's goal is to solve the murder. The goal for a particular scene might be to get the truth out of a witness. The scene doesn't necessarily have to be about the character getting that goal because sometimes other things get in the way, but the character should keep trying to get back to that goal.
There needs to be conflict. This usually comes from someone or something getting in the way of the scene protagonist's goal. It doesn't necessarily mean there has to be fighting or antagonism, just that things can't be smooth and straightforward for the hero. A scene in which the detective interviews a witness who just outright tells him the key information he needs isn't very interesting. Instead, the witness might lie or go off-topic, so it becomes a verbal chess match. Obstacles might arise to thwart or sidetrack the protagonist. The goal might be more challenging than the protagonist realized. I've seen some advice that the character should never actually achieve the scene goal, but if you stick to that advice the story will just end up going nowhere. It might be better to say that the character shouldn't get exactly what he wants or expects. He might get the information he needs from the witness, but it's not the information he expected to get, and that means he has to change plans going forward in the investigation.
Something needs to change as a result of the events in the scene. The characters might learn something that changes the way they see the situation. They might end up in more trouble. They might end up a step ahead of where they were. The relationship between the characters might change. I've seen some writing teachers say that there needs to be a shift between positive and negative in a scene -- if the situation is positive at the beginning of a scene, it needs to be negative at the end, and vice versa. I've found it really hard to consciously make that happen, but it's something to think about if you're analyzing why a scene isn't working.
The scene needs to drive the story forward. The end of a scene should probably generate the goal for that character's next scene. The information the detective eventually gets out of the witness may lead him to develop the goal of finding the critical clue the witness mentioned, for instance. If the character ends up in worse trouble at the end of a scene, the next scene's goal is likely to involve getting out of that trouble.
One other thing to consider is how similar the scene is to other scenes in the story. This tends to happen in stories like quests or pursuits. Each scene in a quest is likely to be about a stage in the journey, while each scene in a pursuit kind of story is going to involve nearly catching the person or narrowly evading capture (depending on who the protagonist is). One scene after another of nearly being caught and narrowly escaping is going to get old, no matter how exciting each scene is, so there needs to be some variety.
In some respects, a scene is basically a really short story that requires a goal, conflict, rising action, a climax, and falling action. It probably won't stand alone as a story because it requires a lot of context, but the structure should work kind of like a story -- perhaps like an episode in a serial. Something needs to happen, and it should make you eager to find out what happens next.