Showing your story to your readers instead of telling it is a cardinal rule in fiction writing, yet much easier said than done. One very effective way to change telling into showing is a concept called motivation-reaction units (MRUs).
What are MRUs? They were first introduced by Dwight V. Swain, in his book Techniques of the Selling Writer. The technique forces the writer to think in terms of the actual action rather than just telling about the action by thinking about your story in terms of motivations and reactions.
- Someone or something does something that affects the POV character (motivation)
- This then motivates a character to do something respond (reaction)
- That reaction becomes the motivation for someone or something else to react to, which, in turn, motivates the character to respond again. (motivation-reaction unit cycle)
Simple, but it can transform your writing.
Let’s apply the concept to a paragraph written in a telling style:
ORIGINAL (telling):
It was eight past midnight, and James still couldn’t sleep. It had been a long day of visiting clients, and he should have been tired. He had climbed into the king-sized bed in his small motel room at 11:30, as was his custom while on the road, but couldn’t fall asleep. After tossing and turning for half an hour, he finally decided that staying in bed wasn’t doing him any good. No matter what he did, he couldn’t keep the restless thoughts and questions that had been plaguing him all week from popping into his head.
MOTIVATION #1: The motivation that starts this all off is the time on the clock. We can think of the action as being the clock “telling” the time, but phrase it in a way that uses an active verb.
The numbers on the clock glowed red in the darkness. Eight past midnight.
REACTION #1: Now we need an action that shows James has been tossing and turning.
James stared at the ceiling for several long moments. After a long day of visiting bookstore after bookstore, trying to convince shop owners to carry his books, he should be dead to the world. Instead, tendrils of an uncomfortable dreams tugged his mouth into a frown.
Finally, he blew out a long breath, then untangled himself from the twisted bedsheets, shuffled across the thin motel carpeting, and snatched his smart phone from the top of the dresser. No sense staying in bed if he couldn’t sleep. Bleary-eyed, he dropped into one of the chairs by the small round table and scrolled through the latest sports scores.
We’re not limited to one action as the response. Sometimes a response a series of actions, thoughts, and/or dialogue.
(James’s Reaction #1 motivates another “action,” this time from the phone. That reaction, then becomes the motivation for James to react again.)
MOTIVATION #2:
Fifteen minutes later, the numbers and words on the phone blurred before his eyes.
REACTION #2:
James chucked the phone onto the bed, then rubbed his eyes. It was no use. Nothing could quiet the restless thoughts and questions that had been plaguing him all week.
Now we can move on to a new set of interactions–motivating actions and character reactions–between James and the thoughts and questions plaguing him as they rise to the forefront of his mind.
REVISED (showing):
The numbers on the clock glowed red. Eight past midnight.
James stared at the ceiling for several long moments. After a long day of visiting bookstore after bookstore, trying to convince people to carry his books, he should be dead to the world. Instead, tendrils of an uncomfortable dream pulled at him.
Finally, he blew out a long breath, then untangled himself from the twisted bedsheets, shuffled across the thin motel carpeting, and snatched his smart phone from the top of the dresser. No sense staying in bed if he couldn’t sleep. Bleary-eyed, he dropped into one of the chairs by the small round table and scrolled through the latest sports scores.
Fifteen minutes later, the numbers and words on the phone blurred before his eyes.
James chucked the phone onto the bed, then rubbed his eyes. It was no use. Nothing could quiet the restless thoughts and questions that had been plaguing him all week.
What a stunning difference! 
In the original, we know what was going on, but in the revision–with its focus on actions and reactions–you see what’s happening. As a matter of fact, it almost feels like you’re right there with James, experiencing his frustration. This is the biggest benefit of deep third person POV. It draws the readers in by putting them into the story.
The reason MRUs are so effective is because they focus on actions. Even if each motivation and reaction is small, as in this example, they build upon each other with actions that show the story. That action drives the story forward and plays out the plot, one action at a time from the hook to the climax.