Well, by holding the up arrow key when hitting the ball, you can manipulate the enemy AI a lot easier.
Also getting the enemy onto one side and then hitting that the ball INTO the wall at that side will make it angle much much more, allowing you to reach the opposite corner very quickly.
Also - shift kinda impacts the angle at which the ball move when hit. As does the direction you are moving. So if you are moving left, the ball will likely move left when hit, if you hold shift too, it will have a 'heavier' angle.