Viewing from the pocket, line up the object ball. Draw an imaginary line backwards from the pocket through the object ball and terminate 1 1/8" past the object ball. In ghostball, that should be your aiming point.
You can practice hitting that aiming point. Stick a donut sticker (notebook looseleaf reinforcement sticker) on that ghostball spot, and one underneath the object ball, and practice aiming for that ghostball spot from different positions on the table.