I'm working a lot on scene design, and teaching a class, so here's a thought to help structure a scene's emotion.
Emotional arc means that there is some change in emotion because of the events of the scene. That is, just as you have PLOT consequences for each event in a scene, you have EMOTIONAL consequences too, only you want to assemble them in a coherent and dramatic way.
Remember that nearly every event is going to cause emotional effects in the POV character. It doesn't need to be a BIG effect, or be described in great depth, but if the hero is insulted and doesn't respond internally or externally in any way, the reader is going to be confused.
The emotional reaction doesn't have to be what everyone else would feel, but there should be something, if only the hero steeling himself so that he -doesn't- actually feel insulted.
But in a whole scene, too, there's a progression in emotion. It might be from a positive feeling to a negative feeling, or vice versa, or from a positive to a different positive or whatever, but it would be an unusual scene where the POV character ends up with the same emotion as she started the scene with.
So, for example, say the heroine starts out -hopeful- about her plan to trap her mother in a lie, then she ends up in a different emotional state because her mother wiggles out of it, or doesn't show up, or proves that she's actually telling the truth. Heroine feels frustrated or angry or guilty, depending on what has happened. There's a change in the emotional content from beginning of scene to end.
Or maybe the hero starts out gloomy about his job prospects, and then in the course of the scene, runs into an old friend who has started a business and is doing very well. So he might end up more optimistic when the friend says, "I need workers I can trust, like you."
One thing I always have to watch out for is making sure that the emotion of the viewpoint character changes in plausible ways, and that I assemble the pieces of the scene so that it's not an up-and-down-up-and-down roller coaster ride of manic-depression. :) That is, if I want her to -end up- feeling guilty, I don't have her start out hopeful, have a moment of feeling guilty, then feel triumphant, then a bit guilty again, then mad, then guilty-- rather that she starts out hopeful of trapping Mom, thinks maybe she's got her trapped so feels triumphant, then mom sort of slips the noose so heroine feels frustrated, then mom lashes out at her so heroine feels angry, and then-- the big event of the scene– Mom whips out the proof that she was telling the truth all along, and that heroine was wrong to distrust her... and then, because of that big event,
heroine ends up feeling guilty.
The arc is building towards guilt. It almost has to happen after heroine gets angry, because the anger at mom makes her mistake/mistrust even more a conflict when she realizes that mom is right. (That is, if heroine had been careful to keep an open mind all along, and kept her temper and not shown her anger, then she wouldn't have much to feel guilty about... so I want to build to anger before getting in the zinger that changes everything.)
So in a scene, I look at the emotional change wrought by the events, and see if there's an arc building to the change, rather then a series of zigzags. It's much more powerful with an arc. I'm actually having trouble with that in the scene in the book I'm writing, but I tend to be able to fix that better in revision. I like to build towards the most intense emotion at the end, and this time I'm hitting "intense" right in the middle instead, so there's something of an anticlimax. I will fix, however. :) I just need to keep in mind as I revise that the scene is more powerful with a coherent emotional arc.