So here's the thing: villains are not villains just so they can twirl their mustaches and say, "Ha! See? I'm evil!"
Just like your good guys, your bad guys have a history. Just like your good guys, they have reasons for doing things. The difference is, the reader tends to not see many of those reasons. Sure, they might get the Sparknotes version eventually, but even then it'll be watered-down; most of the roots of the villainry are trapped below the surface.
Which means they're doubly hard to write.
Villains and antagonists don't sit in the dark corners of their bedrooms plotting ways to be evil. In fact, the most convincing and realistic-and thus terrifying-villains are those who believe that they're the ones doing good; if you told your novel from their point of view, they'd be the good guys.
So when you're writing them, imagine they're the good guys.
What are they fighting for? What do they care about? What do they hope their actions will do? Who do they care about most, if anyone? If they're doing bad, and they know that it's bad, then why? What changed? Try writing a few hundred words of the most pivotal moment of their life. How are you looking at them differently, now?
Bad guys are only human (unless your bad guy is literally not of the human species, but still). They have flaws. They also have feelings. When you're writing your novel, make sure that you're doing them the respect they deserve and show them, and you'll be on your way to humanizing them, because every character exists on a blurred line: nothing's ever black or white.
Think of it this way: villains are the heroes who were never saved. While that's only one possible trope for characterizing your villains, antagonists, and overall baddies (of whatever caliber), it's a good place to start.
So I kind of already gave ya'll my own way of getting to know my villains: write something from their point of view. How do ya'll go about getting to know your bad guys?
Crafting a believable bad guy? Try imagining they're the good guy. Blogger @Rae_Slater talks humanizing antagonists (Click to Tweet)