There are lots of debates over swing plane. The truth is swing plane is rather simple. The club must travel on a more vertical plane versus horizontal. A simple drill and check for plane is as follows. From the setup position, with your elbows resting on you your rib cage, hinge your forearms up with the club. The club should be in line with your trail shoulder. From there simply coil your shoulders back. That is where the club should be if on plane.
To check your plane, simple place a shaft on the ground on the ball line and place a shaft on the ground along your toe line. The but end of the club needs to point somewhere between the two shafts on the ground to be on plane. If it doesn’t point between the two shafts, the club is off plane and will feel much heavier. The club should always feel light and in balance when on plane.