Get into position as if doing a crunch but with your fists meeting each other right at your chin – almost as a boxer would guard their face.
Now, do a crunch, pause at the top briefly and then rotate your torso to one side. As you twist, really squeeze that oblique muscle that is causing you to rotate. After you reach the end of the twist, return to center and then lower to the start position. Repeat and twist to the other side and so on. Remember: up, pause, twist, center, pause, down.