Hitting the ball in the air and keeping a flip allows for unpredictability and can setup Flip Resets and Double Touches. It is also a way to get opponents out of position.
Pop the ball off the wall and make sure the pop hits the ball close to the ceiling but not hit the ceiling.
Boost and jump off of the wall to land on the ceiling. Sometimes you need to powerslide to keep momentum on the ceiling based on your cars direction.
Fall off or jump off of the ceiling. (depends on the situation)
Aim for an aerial hit, flip into the ball, or attempt a flip reset.
Hitting the ball and popping it off of the wall is important for many advanced mechanics. How to hit the ball depends on the ball's momentum, direction, and how much boost you have. There are many ways to pop the ball. Some people brake a little bit before hitting the ball; While others create more distance to the ball when rolling it up the wall. It is up to prefrence and many advanced mechanics have multiple ways to do the same thing.