To quote my favorite Broadway musical, "Are people born wicked, or do they have wickedness thrust upon them?"
Every story has a villain. They might be obvious, like President Snow in The Hunger Games, or (in my opinion) they might be less obvious: a character's own self-destructive nature. Essentially, the villain is the force working against your protagonist.
For the purpose of this post, I'm going to concentrate on the obvious ones: the President Snow's, the Queen Levana's, the wicked step-mothers. In every tale, we tend to see only their bad side: their attempt at gaining and/or keeping power. What the audience rarely sees, however, is the steps in life that led the villains to becoming who they are.
So I ask again: Are people born bad, or is the badness created?
Your villains need a backstory. The catch? You, as the author, are probably the only person to ever know what that backstory is, unless, like Marissa Meyer, you write the villain's story (Fairest, coming out in early 2015).
The trick is to understand that villains aren't bad just for the sake of being bad. There's a reason they are the way they are, and they do the things they do. Looking for their motives will help you understand where they're from, and where they hope to go. It'll help you see why they're bad, or why they want your main character dead.
As already mentioned, a large motivation is power: gaining it, and then keeping it. Your job is to become the psychologist and dig down within their brains and figure out how power became so important to them. Were they orphaned as a child? Maybe they saw their parents killed in front of them. Maybe they loved somebody, once, and then were betrayed. They were wronged in some way, and now they're trying to make up for it.
Figure it out.
Villains are tricky. If you just have a guy with a monocle sitting in a chair petting a fluffy cat, and occasionally laughing maniacally, he's going to come up flat and unbelievable, and more comical than anything. Typically, that's what you want to avoid.
Look at President Snow. Sure, you see him as the guy who wants to keep the districts under his control, and keep the annual Hunger Games happening. This means he needs to kill Katniss, send a message. He's a character who's just a little bit more believable because you, as the reader, understand in book one that there's actually a law that was created about the Hunger Games, which has a base in the conclusion of a civil war that occurred seventy four years earlier. So, now, you understand that in a twisted way, he's only trying to keep the peace.
Most villains tend to believe that they're doing good. They're saving lives, they're creating order. Many dystopian societies revolve around rules and measures that were put into place to ensure the majority's survival. We might think they're far-fetched and too extreme, but to the people leading these societies they're performing a righteous task.
Other villains, in paranormal books, perhaps, might believe themselves to be ridding the world of weakness. Or they have personal vendettas that put one group of people against another in an invisible war that lasts ages. These villains, just like President Snow, believe themselves to be in the right.
I'm not religious, but you can even look at Lucifer (the devil). He was cast out of heaven for challenging his superior, acting on his own pride while believing God to be too prideful in himself. In classic belief of the devil being out to collect souls for hell, he, too, his basically just doing his job.
See, there's four kinds of villains I just explained (I hope?), and the trick is to understand that they, like all of your characters, have histories. Your job is to understand the history of your own villain, and ask yourself why they're the villain, and what happened to make them that way.
Heck, even take Voldemort. He was an orphan who was always picked on by the other kids, so when his magical abilities showed themselves randomly he wasn't sorry. Then, when he found out he was a wizard, he was able to grow and take vengeance against the muggle father that he'd always hated for giving him up. That's a backstory, too.
If it helps, try checking out movies or television shows that chronicle or retell the histories of famous villains. I quotes Wicked at the beginning of this post; that musical is based on the book by Gregory McGuire, which tells the "untold story" of the Wicked Witch of the West. In that tale, the Wicked Witch isn't, well, wicked, only politically misunderstood; she was even best friends with Glinda, the Good Witch. The movie, Malificent, recently came out into theaters, and attempts to explain why the famous Sleeping Beauty villain cast the spell on Aurora in the first place. This fall, Fox is coming out with a new show called Gotham, that follows not a young Bruce Wayne (well, okay, I think it sort of does, in a small way), but the classic villains he'll fight in the future, including (but not limited to): Catwoman, the Penguin, and the Riddler.
Tapping into entertainment like that described above can help you shape your own villains by studying the way others are portrayed.
Remember, when it comes to villains you're probably the only one to ever know the full story. Understanding them to that extent, though, will help you anticipate the way they'll act, and it'll help you create more three-dimensional antagonists.