This article that I wrote originally appeared on Suite101.
Building Toward the Climax
Increasing Pressure On the Protagonist of a Novel
Make the middle of the novel ramp up the tension and conflict and set the reader up for the exciting climax.
Many times, a sagging middle could be because the tension is not increasing, but remaining the same. There are several things to keep in mind to help the middle build tension and drag the reader along for the ride.
Make Things Worse
As you introduce more change and complications to the character, make sure that it all works to thwart the character from his external goal.
Each obstacle should make it harder and harder for him to reach his goal, making his situation worse and worse. This increase in trouble will increase the tension of the story, and increase reader interest.
Strive for the unexpected and unanticipated when you add conflict to the story. Drop surprising disasters on your character. This doesn't necessarily mean explosions or dead bodies, but strive for creativity in the events that will twist the story in ways your reader never expected.
Avoid General Conflict
Try to avoid simply "bad things that happen" to the character that have nothing to do with the external goal, or complications that only delay the trouble, not make them worse than before. Make sure all conflict works directly against what the character wants to accomplish.
Strive for constant change in the story. The hero is continually thwarted and must continually adjust his plans to attain his goal. If you have an antagonist, also make the antagonist continue to adjust his decisions in reaction to the protagonist's actions.
Give the Character a Strong Crucible
Make sure your character has a rock-solid motivation for continuing with the story rather than just quitting. There has to be a Crucible that makes her stick with it, that doesn't even give her the option of turning back—the "doorway of no return."
Make the Opponents Well-Matched
If the fight between protagonist and antagonist is balanced well, it makes the conflict more interesting to the reader. Give your hero an "equalizer"—something that gives him an edge so that the fight isn't entirely one-sided. Think David's sling and his unwavering faith in God that equalized his fight against Goliath's size.
Make the Stakes High
Make the character have something irreplaceable that he could lose. It will increase the pressure on him to win, which will increase the tension and reader interest.
Don't limit this to the protagonist—give the antagonist equally high stakes. Any character who contributes to the conflict should also have something precious to lose, which will solidify character motivations.
Steadily Increase Intensity
Make each complication have greater intensity and more at stake than the last complication. Create rising tension and doubt in the reader about if the hero will achieve his goal.
Map out the story's major disasters and make sure they're in rising order of intensity and disastrous effects. If your middle disasters are worse than your later disasters, consider switching them or finding a way to make the later disasters even worse.
Box the Character In
This is the most important of all these tips. As the story progresses, take away the character's choices. Restrict his actions and the decisions he can make. Slowly take them away until he's left with few choices at the climax. A good visual is to picture forcing your character into a bottleneck or a funnel.
All these things will help you build the tension in the middle portion of your novel.