Most times, writers spend much of their time and effort crafting a compelling main character and do a lazy job of presenting him with an equally fascinating antagonist. The aim of an adversary is never to steal the shine from your hero. Yet, a villain needs some attention to be impressive, which eventually shines more light on the protagonist and makes his journey more riveting. To create such an impressive villain, there are some steps you must take: you need to plan, create the profile of a worthy opponent, and make his actions believable.

Some writers let the story write itself. They have an idea and just make a mental dump of it on paper and leave the heavy lifting to the editing process, which weeds out a large chunk of what they have written. Then they get a better idea of what the story entails and try to fill up the holes or even start all over again. And they hardly know who the villain is until they have to create him. 

Perhaps that's the type of writing process you need to flesh out your story ideas. Or maybe you are the opposite who plans everything down to the last detail before they begin to write. Or you are somewhere in the middle. 

Whatever method works for you, to create a worthy villain of your main character, at some point, you will need to plan exactly who the villain is. A good villain, like a good protagonist, does not just happen, not even when you are a free writer; either your pre-writing or post-writing process will need you to plan out. So, make time to plan your villain.

In planning your villain, you need to make sure he is worth the time and effort of your protagonist and your readers. Readers want a worthy opponent, not one whose defeat came with the flick of a wrist. 

The villain must not necessarily be a flat character who is deplorable and annoying; it is more compelling when your antagonist is complex with a backstory. He could be the victim of his environment. Maybe, he does what he does because he has no other choice. Or, in the case where you have an antihero, the anti-villain could just be doing his job. 

The point is that your villain needs motivation, a strong reason for opposing the protagonist. And he needs self-justification for his actions, except he is a psychopath who inflicts pain just for the heck of it. Even psychopaths believe they are doing the world a favor, so your villain should not be any different. Your villain also needs a backstory that explains why he is the type of person he is, a person who would stand in the protagonist's way. It could be something in his childhood or his early life experience.

Though most of the information in your antagonist's profile will not make it to the story — typically, only about 10 percent does, and some stories don't give him enough scene time to the villain — yet knowing all this helps you create a villain that lives beyond the pages of your story.

Next, in creating your villain, you need to make his actions plausible. Let his crimes or tactics fit his personality. A fragile teenager with no history of gun use cannot just, all of a sudden, be a mass shooter with a machine gun and a rocket launcher. There has to be an explanation for how he could achieve such things. Your villain must have the capacity to be the person he is and do the things he does. 

Also, there needs to be the right circumstance behind your villain's action. A hired assassin just doing his job doesn't kill a person the same way as a high school shooter who hates his school and wishes everyone there dies. A vengeful person kills differently from a professional killer, and a crime of opportunity differs from a calculated offense. So, the factors surrounding your villain's offense need to be adjusted to fit the offense.

When you put all these in place, you have yourself a compelling story with not just a compelling character but a remarkable villain that makes it a lot more interesting and keeps your readers flipping from page to page.