How to write scenes

Characters & Action

Scenes with characters are usually more engaging than those without as it offers us somebody to relate to. A volcanic eruption destroying an island is awe inspiring, but we can't relate to a volcano. Add a character's thoughts and point of view to it, and the scene immediately has a bigger impact. But the character within a scene doesn't need to be human for this to work. Simply humanizing something part of your scene will do the trick. Even the volcano could work, as Disney-Pixar's Lava short did, for example.

Simply having characters in a scene isn't enough though. There has to be a character who is driving the scene forward, a character who isn't simply a passive bystander. This doesn't mean the character has to be on the move or even has to talk, but they have to engage with whatever is happening so the reader is engaged through them.
In the volcano example, an engaged character might feel fear in the presence of such raw, natural power, and feel sadness for the destruction it is causing. They might try to keep their balance as the ground shakes violently or seek to avoid falling debris.
If a character is bored or indifferent to what is going on, the reader will be bored, too. Either because they empathise with the character and feel what they feel, or because the scene is boring in and of itself.

Diversity of Action

Having a character engaged with what is going on is only the first step. The actions they perform should be varied, too. This is more for the reader than for the character, as a character could be doing the exact same thing for the entire scene while still being described as performing different actions. To illustrate this, picture a character observing guards guarding a house from afar. The scene could be described in two ways, the first of which is wrong:

For the better part of the afternoon, Eline observed the people guarding the house. She saw 12 in total, 4 of whom had bows and arrows, the others only swords. She watched their movement to see if there were any patterns and made note of them. Besides the guards, she saw several staff members enter and exit the house, and the target's wife attending the vegetable garden. It wasn't until the sun set and it became too hard to see, she returned to base.

For the better part of the afternoon, Eline observed the people guarding the house. She counted 12 in total, 4 of whom had bows and arrows, the others only swords. She studied their movements and wrote down any patterns she discovered. She also kept an eye on the staff members who entered and exited the house, and made special note of the target's wife attending her vegetable garden. She returned to base just after sunset.

The reason the second example is better than the first is the choice of verbs. Take a look at all of Eline's actions in terms of the chosen verbs.
First example: observed, saw, watched, made note, saw, returned. (There's also two more mentions of 'to see' that apply to her, but aren't actions she took.)
Second example: observed, counted, studied, wrote down, discovered, kept an eye, made special note, returned.

Imagine each verb and notice how they all evoke a mental image or a specific movement, even in the vacuum of a simple thought. In the first example there are only 3 types of them: watching, making a note and returning. In the second example there are 5 (arguably 7) of them: watching, counting, writing, discovering, returning, and arguably studying and making special note of.
Using the same types of verbs means the same types of mental images, which gets boring fast. It's similar to using "she said" over and over in dialogue. Simply changing the actions you describe go a long way to make a scene more engaging. Nobody ever only does one thing as they're more than just a pair of eyes or a mouth or a pair of hands, so there's always plenty to use to break up the monotony.

To be or not to be

On the topic of verbs evoking mental images, the exception to this is the verb "to be". It doesn't evoke an emotion or a movement, it just is. This means using "to be" should be done carefully, as there's usually other verbs that could be used instead and will evoke far more powerful images. For example, instead of "the mountain was in the middle of the desert" you could use "stood" or "sat" or "rested". Instead of "the tree was immense" you could say "the tree towered above all" or "the tree watched down from high above" or "the tree reached for the sky". Using verbs this way allows you to set the scene in a more evocative way and have it play out in a more captivating way.

This doesn't mean you should avoid "to be" at all costs, but simply consider other verbs you could use. Often you'll find you're able to convey a lot more information this way, without having to increase the word count, which is incredibly valuable regardless of whether you're writing a short story or a 6-book epic adventure.
In some cases it also allows you to explore characters more. "He was excited to see her" could be written as "He couldn't wait to see her" or "He counted down the days to see her" or "He ached to see her" instead. Each evoking a different image specific to a different type of character.

Narrative Action

Alright, let's shift our focus back on the scene as a whole. Just as the actions of the characters matter, the actions of the scene as a whole matter, too. By this I mean all the actions that happen between the very beginning of the scene and the very end.
Scenes are smaller stories within the story as a whole; they're the series of events from beginning to middle to end. But they in turn have a beginning, middle and end as well. With this in mind you can dissect a scene and see what happens within it more easily. Has the story overall progressed from the scene's beginning to its end? If not, there might be some issues with the scene.

A first thing to note is that the story overall in this context means the "present" of the story. Flashbacks, back-stories, etc. can be important parts for the reader, but they themselves do not progress the story from the point of view of the characters. So a scene entirely made up of back-story is best avoided. It's what usually comes to mind when people think of forced or too much exposition.

This doesn't mean there can't be scenes heavy on exposition though. The trick, like any scene, is to involve one or more characters. Their thoughts and feelings regarding whatever exposition you're giving is a powerful tool, as is their reaction to any exposition discovered by them. A person studying a book in a library, for example, could be a scene heavy on exposition. But the way the person responds to everything they read changes everything. What do they think of the information? How will they use it? Does it contradict what they thought they knew? Are they able to stay quiet or will they feel the wrath of the librarian?

Keeping beginning, middle and end in mind makes it easier to have your scene flow like a river rather than be straight like a road. With rising and falling action you can add parts of suspense and parts of relaxation to your scene. Within short scenes this can be very relative though. It could be nothing more than getting a question answered, for example, with the moment leading up to the answer being the rising action and the effects of the answer on the character being the falling action.

Location

Something sometimes forgotten or not focused on enough is the location of a scene. It may seem like a strange thing to forget, but it's important to make sure a scene is grounded in the reality of your story universe. If the reader doesn't know where the characters are, the scene will essentially play out in a void. Plus it can be described at many different moments with different effects. It could be used to set the stage at the start, it could be used to split up sections of long dialogue, it could be used to telegraph or foreshadow upcoming changes or events, and much more.

But location is more than just grounding your scene in a reality. Describing the location is a little like setting the mood in a room. Just like a room's mood can be changed depending on what items you use to decorate it with and what lights you use to light it with, so too can a scene's mood change depending on what parts of a scene's location you describe.
The same perfect summer day could have a description focusing on people enjoying the warm rays of light, or on a flower wilting in the scorching sun, or on a pond's water drying up too soon, or on clouds growing on the horizon, and so on.

Heart of Your Story

One final element that makes it easier to figure out whether a scene is working or not, is to keep the heart of your story in mind. What is the big overall conflict or question you're trying to convey? There can be more than one, different characters usually have their own conflicts to resolve after all. But with these questions in mind, ask yourself if your scene contributes to solving these questions or conflicts.

The library scene I mentioned before could both work and not work depending on the greater context of the story. If the character learns knew (plot relevant) information, the scene works as it drives the plot forward. If the scene is only there to showcase the character loves to learn or is book-smart or something similar, the scene doesn't really work as well as it could. Giving character info is great, but it can be done while the plot is driven forward instead of pausing it for a character moment.

Pacing

The last thing to keep in mind is pacing. However, pacing is a large topic in and of itself so I'll cover it in a separate guide in the near future. For now the main thing to consider is how fast the action is taking place in both a time passage and sentence structure point of view.
Some scenes benefit from quick actions or descriptions that skim over over minor details to make time pass faster, while other scenes are ideal for dragging out every second. A regular conversation and an interrogation scene are two examples of these contrasts, but not all scenes are as straight forward.

Consider what you want your scene to convey and what you want your reader to feel. A straightforward action scene could be fast and surgical; each punch and kick are described quick and simple to convey the speed of the battle. Or it could be described with character thoughts in between each hit, perhaps when a character is being physically tormented by a bully. Or it could be described in an analytic way from the point of view of a character who's dissecting their opponent's moves to find an opening to strike.
Keeping this in mind goes a long way to kick your scene up a notch. Reread your scene and ask yourself if it feels too fast or too slow in relation to what is going on and how you want it to come across. Then rework it as needed.