Basically, all you want to do is throw the puck at the net, it's a simple concept. Before I tried making my shots look pretty. When really it's quite simple. Get the puck, throw on net.
For slappers, all I do it to fire it off hard and on net, I get it pretty low from the blue line but it's a really hard shot. My bro is more keen on making his shots go shelf, but the shots are really weak and are often off target.
Always keep in mind, Throw it on net. Imagine throwing a baseball, but instead of your arm throwing the ball, your stick is throwing the puck.
*shrug*