Move near the goal post. If anyone tries to tackle you, leg it and go the goal post. Press Square and the ball should go in.
Edit your favorite team's statistics. You can make everyone in that team be the best with a 99 rating for shooting accuracy (for example). You can do this to everything.
When your have the ball, do not move the player. Instead, quickly press R(3). The player will do a trick automatically. Note: Players with low skill levels may not be able to do this.