The harder the shot you are taking the further apart your hands should be. For example for a wrist shot your hands can be a close as a 12 inches, but if you are taking a slap shot you are going to want at least double that (24+ inches).

Remember that large portion of your shot speed is generated through the whipping action of the stick, the more whip you can generate the harder your shot will be.

The science behind this concept is covered by one of the basic tenets of physics: every action has an equal and opposite reaction. This is why you want to hit the ice about 6 inches behind the puck, this allows your stick to load up on kinetic energy (flexing away from the puck), which is then released and snaps the stick back towards the puck.

One of the best goal scorers ever in the NHL, Brett Hull, is a perfect example of this. Watch just about any goal of his and you will see a huge amount of flex in his stick, which then snaps back to its resting state and transfers all of that energy into the puck, which equates into a very powerful and accurate shot.

So how does this relate to your hand placement? Where your hands are on the stick will vary the amount of energy you'll be able to transfer into the stick. The closer your hands the less power you'll be able to transfer, where as the further apart your hands the more you'll be able to transfer.

Keep in mind that there is going to be an optimal distance depending on your technique, remember that your hands are just the transfer point you want to make sure to use you large leg, core and upper body muscles to power your shot.

When taking any shot, wrist, snap, slap or backhand you want to transfer your weight from your back leg to you front leg - and in the case of a slap shot almost explosively (you should almost feel like you are falling on your follow through).

The more weight and power that you can transfer into your stick, the more weight and power (energy) will be transferred into propelling the puck.