As an author, it is crucial that you know when it is the time to pick up the pace of the book, and when it is time to slow down and linger. This is all done through not just the amount of information you provide to the reader, but also in the structure and length of the sentences, paragraphs and chapters.
I am sure you have all had this happen to you before. Someone starts telling you a story about something that happened to them recently, or maybe it is someone trying to give you instructions for how to do something. In your head you are thinking, "this should be short and sweet!" Get the information and move on. But nooooooo.... There is this point that your brain starts thinking, "Come on get this moving! We could have moved on by this point and we aren't even close to the conclusion!"
That's poor pacing.
WHEN TO KEEP IT MOVING
Keeping the story moving is often tough at the very beginning of a story. Most of this is due to the fact that the author has so much information flowing through his or her head that they want to get it all down on the piece of paper fast. The problem here is simply a situation of the opening now being an informational dump.
To control this, consider that information like the military. We give out that information on a "need to know basis." Yes, we understand you needed to understand all of the information, but do your characters really need to know all of that information?
Consider the Lord of the Rings, or The Hobbit. Tolkien had to create in his head the entire world of Middle Earth. He had to know where the rings came from. He had to know who was living there and their interaction with each other. But for the reader, we simply needed to know what Hobbiton looked like and who the Hobbits were, especially Bilbo and Frodo. They weren't concerned with the whole history of Middle Earth and guess what? The readers don't either. We can get that information later.
We have a foreign exchange students staying with us right now. We have been taking him on all of the local tours and sights since he arrived. But when it comes to knowing about things about the region, or even about our family, that information comes out at the time we are at that location. We told him about the Seattle fire WHEN we were in Pioneer Square and saw the sign for the Underground tour. We told him about the history of the Space Needle WHEN we were waiting in line to go up.
We can also keep the story moving through those tense and emotional scenes. This is really done through the balance between the dialogue and the narration.
If you consider when people are in the middle of an argument or a heated conversation, there really isn't a whole lot of time to think. The words just keep coming. What you will also notice is that sentences tend to be shorter and less complex.
Finally, we want to keep the story moving through longer time sequences. This is the space in your story that happens between those two key scenes you have put your characters into. For example, the characters just had a romantic dinner and now are eager to get home and get to "dessert" (so to speak). We do not need to know anything about leaving the restaurant, walking to the car, the ride home, the traffic, the music on the radio, etc. Have them simply look at each other over the empty plates at the restaurant, throw in a chapter break or a * * * and then launch into the "dessert".
Over the empty plates and half-filled wine glasses, Melvin and Mertes knew that dessert was going to happen as soon as they got home.
Slowing it down is simply those chances to let the reader into the heads of the characters. This is the place where we get the depth and the introspection. This is where we are truly sucked into the story. Unfortunately, authors really do miss this one. I do think this comes from being told too many times to keep the story going. The end result, however, is the lack of information.
I have talked in the past about the idea of monologues. Shakespeare used this idea so well. He would frequently take time to give the hero or heroine a chance to explore their thoughts and emotions. We were really listening to those thoughts that are normally silent in the characters head.
After those action scenes, or after those intense moments, the reader needs a chance to think about what happened.
It is in these moments you need to expand on your thoughts. These cannot be one liners but full paragraphs of material. It is here when the character can think back to an event that happened in their past and realize that was the reason for their behavior with the character just moments before.
When it comes to those sensual scenes, you can slow it down here to. If you want to create that strong sense of passion, forget the "quickie" and let them enjoy. Please note, however, this is not a time to think and it is certainly not a time of world building or introspection. Focus only on the two characters and what they do.
Now you don't need to do this. If you want to tone down the sensuality of the story, just send them behind closed doors and then wake them up the next morning with a smile on their face.
There really isn't a right or wrong approach to controlling pacing. Just be aware of what you are including. Be aware of the sentence structure. Be aware of the information dump. And most importantly, think like a reader. Are you going to start thinking, "Oh my gosh, just get on with it?"