Have you seen the recent Joker movie yet?
(Not really a spoiler, but just in case)
There a scene where the Joker gets condemned for committing murder. The Joker responded something to the effect of "why should I care about those people I killed? None of you would care if I was murdered on the streets!"
I think that's a good insight into the mind of a cruel/villainous character. A character like the Joker believes his actions are justified, no matter how morally reprehensible he may behave. He has dreams and goals like the rest of us, the only difference is characters like him don't play by any rules.
A trick I think to writing a good villain is to make the character somewhat relatable/sympathetic to your audience, versus writing a caricature villain who does evil for the heck of it. If really successful, some of your audience may not even consider your villain to really be the "bad guy" of your story.
An example that comes to mind is the alien character Scorpius from the TV show Farscape. On the surface he appears to be the typical villain: he has no qualms with torturing and/or killing people. However, upon closer examination his character is a bit more complex. He's the product of a brutal rape, he was tortured constantly as a child, and the only life he's known is "the strong survives and the weak dies". His ultimate goal isn't personal power, but rather to save his mother's species from being exterminated. If he needs to kill or torture to accomplish this goal he'll do it, but he will also cooperate and negotiate to succeed as well.