In any kind of one on one situation with a keeper, the keeper must move towards the attacker on a line that runs from the ball through the center of the goal, thus narrowing the angle and reducing the area of the goal that the attacker is able to target.

If the ball is outside the reach of the attacker you should move towards the ball as fast as possible. If the attacker has full control of the ball you must be more cautious and watch for the chip or an attempt to dribble around you. If the attacker is coming from something of a side angle, then attempt to force him wide of the goal.

You must always be ready to hit the ground or the air to stop a hard shot. If the attacker glances down at the ball it may indicate a shot soon, but you must always focus your primary attention on the ball itself. Once you get close enough, you must attack the ball, getting your whole body sideways and in front of the ball. Even a deflection touch with your hand may be enough to save the goal once you've narrowed the angle down sufficiently.