After release, your hand should be in the same position as if you were shaking hands. You don’t need to overdo it, and if you do, it could cause injury. If your hand is in the same position as Kelly Kulick's, above, you're in good shape.
The more you bowl, the more control you’ll get over your hook, and you can adjust these tips accordingly to fit your game. Every bowler is different, but these general principles should give you a good start on hooking a bowling ball.