Shoot wide rather than high
Shoot low
Keep your body over the ball
Keep contact with the middle to top half of the ball
Keep the player in front of you
Stand the player up and don't dive in
Focus on the ball when defending one on one
Bend your knees and be on your toes at all times to be more agile
Don't stand flat footed: that is how you get beat by the forward on the opposing team.
Eyes on the ball at all times
Don't stand too far away from the goal
Have confidence!
Have good hand-eye coordination.