Gripping the golf club hockey-style isn’t recommended on the course, but practicing this way can teach you to correctly rotate the hands and fix your slice. It will increase your power, too.
Here’s the drill, which does not require hitting a ball:
Note the position of your right hand at the finish – it’s beyond the left hand, with the right arm straight. To overtake the left hand, the right had to move faster through the hitting zone. That’s the motion you want in your regular swing.
Next, move the right hand up to the bottom of the handle, with the index finger just above the shaft; keep your left hand in its original spot, with a little room between hands. Make 10 more swings.
Now place your hands together in your typical grip position. Try another 10 swings, rolling the right hand over the left. As you follow through, the back of your left hand and the clubface should point to the ground.
Finally, start hitting short shots, emulating the same release action through impact. You should see the ball fly straight and perhaps draw a little. Try to roll the hands over quickly and forcefully enough to actually hook the ball hard to the left.
Once you can control the club well enough to hit a hook, you’re on your way to curing that awful slice.