Accuracy is the most important part of shooting in any sport, and it is especially important in hockey because hockey nets are relatively small compared to those used in soccer, for instance, and goaltenders are often able to cover the entire net when they are playing their angles correctly. Shot accuracy is a skill that any player can develop with practice.
The best way to improve shot accuracy is to shoot for a target every time you take a shot. If you're just flinging pucks at the net or shooting as hard you possibly can without aiming for a specific target then you will develop very poor shooting habits that can be tough to break. Shooting targets are fairly inexpensive and are a great tool for developing a more accurate shot. It's also very important to practice shooting at the net from many different angles. Very rarely will you find yourself wide open in the slot with the goaltender out of position. That's why it's important to be able to hit the net from anywhere on the ice.