Most golfers have difficulty getting the ball to start out in the direction of the target. The initial direction of the golf ball is determined by the path that the clubhead is moving along through impact.
The typical problem that most golfers have with respect to their swing path is an out to in path through impact. This out to in path produces off center hits, pull shots and slices. This out to in path is a result of a lack of rotation during the backswing and an improper unwinding sequence of their body. It is very important to allow the shoulders to rotate during the backswing. This rotation allows the hands to swing behind the back shoulder at the top of the backswing. Allowing the hands to swing behind the back shoulder at the top of the backswing creates the angles necessary to approach the golf ball from the inside.
I personally believe that golfers feel that the swing path should be a straight line. This idea of a straight line produces the out to in swing path. Instead, the golfer should view the path as a circular type of motion. The clubhead should approach the golf ball from inside of the targetline, squaring up through impact as a result of the turning motion of the hips and then back to the inside just after impact. This rounded path with a small flat spot around the golf ball produces the path necessary to achieve a consistent directional path with the flight of the golf ball.
An excellent way to develop this inside path is to set a headcover on the ground just back behind the golf ball, maybe eight inches. Then begin to hit golf balls without striking the headcover. The sensation developed will be one where the golfer feels like they are swinging out to the right of their target, but the golf ball will fly straight towards their target.
Occasionally, a golfer will produce too much of an in to out swing path. This typically is a result of a lack of forward swing body rotation. For this golfer, make sure that you are allowing your hips to clear out of the way, rotating towards their intended target. This rotation allows the clubhead to square up down the targetline through impact.