Spend some quality time characterizing your antagonist.
Novelists, as you create your story, keep in mind that your antagonist is just as important as your hero.
Without Darth Vader – there is no Star Wars franchise.
Without Moriarty, Sherlock Holmes isn’t challenged to fully utilize his formidable detecting powers.
Without Voldemort, Harry Potter’s life becomes a walk in the Hogwart’s park.
Your antagonist must be a force to be reckoned with. And he should not appear to be a cardboard construct. Just as you take care to create a hero that pops off the pages in life-like detail for your readers, so too take care to create an antagonist as fascinating as your hero. The stronger your characterization of your antagonist, the better your story.
Clearly, the shark in Jaws, Voldemort, and Darth Vader contribute mightily to the success of the stories in which they appear.
That, of course, is because the more formidable the antagonist, the greater your hero’s heroism in standing up to him or her – and the better your story.
Give your antagonist a compelling motivation for his actions.
Keep in mind also that strong antagonists have strong motivations. A villain’s usual motivations? Greed, revenge and/or a desire for power – often with a touch of madness thrown in for good measure.
But, in some stories, the antagonist may technically be on the side of the angels.
Remember Lieutenant Gerard in The Fugitive? Gerard is the FBI agent who is determined to recapture Richard Kimble, a doctor who has been wrongly accused of murder and who has escaped. In his dogged efforts to enforce “justice,” Gerard hampers Kimble’s efforts to find the real murderer. Gerard is ostensibly motivated to do what’s right, but ego is a large part of his motivation as well, and his behavior appears obsessive/compulsive – which makes him a formidable, complex and interesting antagonist.