This drill is designed to slowly build up the technique and strength that the goalie needs to make full and quick steps out to the ball.
Set up two parallel lines approximately 3-3.5ft apart from one another.
Without a stick have the goalie start lined up perpendicular to those lines (see diagram) and begin making controlled full steps.
These steps should resemble lunge jumps in which the opposite foot pushes off hard into the direction of the ball to get optimum distance.