For a smooth, modest hook and one which is simple to control, set up the approach with your hand holding the ball not flatly underneath the ball and not entirely on the side of the ball as if you were going to shake hands with any person, but rather in between the two positions.
If you were to permit your hand to maintain this position via the full swing cycle and into the release area, you would rotate the ball’s axis, perhaps just 15-20 degrees, and the outcome will be a controllable hook on the back end of the lane.
You can also grip the ball in a full handshake position or on the side of the ball and maintain the position via the swing and release to get a similar outcome.
Still, the danger is that you may “over-turn” your hand and blowing elbow while releasing the ball to have your hand pass over the top of the ball and your palm of your blowing hand face the floor.
That kind of release will definitely cause inconsistencies and outcome in a bad direction towards the target and an unsuccessful roll.
By all means, keep your bowling hand positioned between the flat and handshake, palm up positions all through the swing cycle, and the release with your elbow directly behind the hand entering the release area.
Ball Release | USBC Bowling Academy
You will get a perfect and moderate hook on the bowling ball.
It is easy to get a sharper and more powerful hooking motion on your ball by setting up on the approach with your hand under the ball with the palm of your hand facing toward the ceiling.
This kind of hand position is generally as “behind the ball” positioning as your hand gets the critical release area with your hand, maintaining the “behind the ball” positioning on the forward swing.