Think about the cartoons you used to watch as a child. There was always the good guy, who had an awesome lair, cool weapons, and interesting personality quirks. They were the most interesting character in the world. The show literally revolved around them.
And that was probably ok with you. Meanwhile, the bad guy couldn’t have been a simpler character. He’s a villain because he’s bad. It’s as simple as that. But why is he bad? Did he have a bad childhood, a traumatic life event, or deeper motives to carry out all of his evil plans?
Sure he does. Why wouldn’t you tap into that bottomless pit of despair? There are so many dark, rich concepts to explore. Give your protagonist a break in the story. Let him take a breather, and dive into the lives of the other characters in your stories.
A good exercise to practice this is to actually write your story entirely from the point of view of your antagonist. Structure the story like you normally would, develop a natural plot, but tell it from a new and unexpected perspective. Give all of your characters depth, and you’ll be amazed at how many interesting concepts present themselves. Things you’d never have expected.