One of the keys to a powerful, accurate wrist shot is to keep the blade of your stick in a straight path towards the target during the entire shot. The angle of your stick blade should also remain as flat to the target as possible.
It's a lot harder to control the direction of your shot when the puck is traveling in an arc-shaped path around your body. Changing the angle of your stick blade during your shot adds yet another factor that you have to compensate for. You golfers know exactly what I'm talking about.
Here's a great shooting tip I was given at my hockey skills class a few weeks ago.
When you bring the puck back behind you, move your front arm across your body, so both your stick and your front hand are behind you. With your stick now lined up with your stick blade, it allows you to tilt the blade of your stick over the puck and keep your stick blade perpendicular to the target.
Keep your stick in line with your blade throughout the shot as you transfer your weight to your front foot. Roll your wrists over to shoot and point your stick where you want the puck to go on the follow through. Shoot low for the rebound!!
Notice how her top hand is back across her body, and her stick stays in line with the stick blade throughout the shot.
If you keep your leading arm in front of you (like I was doing) you're forced to change the angle of your blade when you try to tilt your stick to cup the puck. With your arm out in front, you have to move it out of the way in order to keep the puck in a straight line towards then net as you follow through. Either that, or you push the puck in an arc-shaped path; first away from you, then towards at the end of your shot. No wonder I can't shoot straight!
Line up 10 feet from the boards along the blue line and aim for the blue line paint up the boards. Keep the puck straight along the blue line for the entire shot. It may feel awkward when you first try to shoot this way, but the improvement in power and accuracy is almost immediate. I had to force myself to shoot this way in the pre-game warm ups for a few weeks before it came naturally. I still revert to my old method when I panic, which unfortunately, is a lot.
Try it, I hope it helps!
Here's a few more Shooting Tips
CBC Shooting TIPs
USA Hockey Shooting Tips
Whockey Shooting Tips
Dunedin Shooting Tips
Hockey Tips: Backhand Shot