So you have convincing “attention-gatherers” in your well-crafted characters, and you have some idea of how to make their world seem real. The only way you can really go wrong now is to trip your reader up with some unforeseen obstacle or missing information, especially when things pick up pace, when the motion changes in rhythm.
To avoid this, try to walk with your reader through the world to which you’ve introduced them: there must be some kind of logic to what happens, and your readers must be “anchored” in some way to avoid confusion. They will be too distracted if the complicated plotline becomes so complex that they lose track of it.
The novel Jonathan Strange and Mr. Norrell almost betrays the reader in this way —just as you think you’ve grasped how things are going to resolve, another new idea or tangential plotline is introduced. Luckily, author Susannah Clarke pulls it off and the finale is grand and gripping, but some writers don’t quite manage a successful ending because they have not walked us through at the right pace so that we can appreciate what is going on. If we’re on a bus-top tour of London, we don’t want the bus travelling so fast that we miss half of the sights; nor do we want it to wait for ages at a stop. Pace it at about “walking speed” even when the action described is fast.
In his Bond novels, Ian Fleming demonstrated a control of the technique, as in this short excerpt from Doctor No:
It was six-seventeen. With a squeal of tyres, a dingy motor hearse with black plumes flying from the four corners of its roof took the T-intersection into Richmond Road and shot down towards the group on the pavement. The three men had just had time to pick up Strangways's body when the hearse slid to a stop abreast of them. The double doors at the back were open. So was the plain deal coffin inside. The three men manhandled the body through the doors and into the coffin. They climbed in. The lid was put on and the doors pulled shut.
It’s all to do, ultimately, with rhythm. In the eight sentences above, the majority are short; there are scarcely any adjectives or descriptions to slow pace; the structure of each sentence is simple, and the action is precise. Fleming doesn't have to describe every movement in much detail to convey a complete sense of what s happening nor to maintain tension —in fact, it is precisely this which keeps the drama going.
But look at another key factor: see how Fleming anchors the reader in the above passage by focusing on the hearse and its contents -- its description, its motion, where it stops, its double doors, the coffin. So the reader can glide through the action without losing focus.
Successful action scenes focus on one or two key viewpoints, objects or images.
It's crucial, though, to communicate the most important steps, or you’ll “miss a beat”. Each part of the action is mentioned; nothing is left hanging. In action sequences, the reader needs to know the steps taken, one at a time. But they are all draped over one or two key points so that readers don't get lost.
Nothing spoils suspense for a reader like losing the sense of what’s happening.
Anchoring the reader avoids this.