Do you have an antagonist in your story? Not every novel embodies an antagonistic force in a person, someone who works directly against your main character. But it’s a useful tool. The opposing character adds energy and tension to a story.
The villain on stage
If this is your fictional choice, why keep the villain off-stage? Even literary novels such as Dan Simmons’s The Terror, use villains to great effect; in Simmons’s case, the pompous Franklin and also the smarmy and horrific leader of the mutiny. They are brought to life by giving them dialogue and interaction with the main characters and in subplots. They have real work to do, and we see them do it.
Connecting the hero to the antagonist
One technique that should be used judiciously is to give the antagonist a physically separate subplot that only connects with the main character’s at the climax. It can work, but why save all the delicious clashes for the last moments of the book? Allowing your hero and your villain to cross swords in early verbal sparring can delineate your theme, throw your main character’s strengths into relief, and allow your villain to justify himself, lending shading to his character.
Provide contrast to the villain
If you must keep your hero and antagonist separate, then you might consider giving the villain a charged subplot occupied by a stand-in for your hero. That is, a person who provides a contrast to the villain and can pull out of the scenes the depths, doubt and tension that a behind-the-curtain-opposition will lack. I used this technique in A World Too Near, with Depta, the long-suffering attendant to Lady Chiron.
I know we don’t want moo-ha-ha villains. But let’s not be afraid of trying our hand at tension-inducing antagonists. Let’s consider bringing him on stage a bit more and making him an intriguing, or at least infuriating, figure.