Whenever possible, it's best to get control of the ball; catch it with your hand rather than blocking it with your hurl. There are always full forwards lurking at the edge of the goal box, watching for chances to pounce on loose balls; part of a goalkeeper's responsibility is to deny them these second-chance opportunities. But, if catching the ball in your hand isn't feasible, knocking the ball hard away from the goal will likely send it past the line of eager forwards. Trust in your fullbacks to clear the ball away for you.
Positioning
In general, the goalkeeper should be positioned in the center of the goal, as seen from the perspective of the offensive player taking the shot. If the shot is coming from the wing, the goalkeeper will shift towards that wing.
Several factors, though, can cause you to adjust your position to one side or another, anticipating where the shot will go. First, watch the feet of the player taking the shot. As long as the shooter isn't shooting on the run, the line of their feet will indicate the ball's most likely path. Second, if a player is shooting on the run, crossing left to right relative to the goalkeeper, the ball will likely also travel to the right. Finally, pay attention to lines of sight. It's no use maintaining position in the center of the goal when another player is blocking your view of the ball. Not only does it make you useless, the ball isn't likely to go through that player's body anyway. A smart forward will be looking for an open path to the goal; the goalkeeper needs to find the most inviting path, and fill it.
Coming out of goal
You should be ready and eager to come out of the goal box to make plays. The surest way to stop a goal is to keep the shot from ever being taken. Any time you feel that you can be the first player to reach a loose ball, you should go for it. The goalkeeper has a big advantage: nobody from the opposing team is marking you, contesting every play with you, everywhere you go. This gives you a freedom of action which you should exploit.
MENTAL
GAME
by Joel Travis
photo credit: Kerry Leonard