Basically, your protagonist and antagonist each want to drive the plot. They’re fighting for control of the steering wheel.
If you remember that every villain is a hero, it’s often helpful to look at the whole story from the other guy’s point of view. Don’t just ask what the villain wants. Ask what the villain needs. Look for an arc so that he can change as well.
That doesn’t mean you ultimately have to split your time evenly between hero and villain. You almost certainly shouldn’t. But knowing what that guy’s movie would be can help you find the best story overall.