When hitting a ball from a green side bunker it is important to understand the physics of the shot. First of all remember your target is not the ball itself but rather the sand a selected distance behind the ball. The ensures that the following occurs. Club hits sand - Sand hits ball - ball leaves bunker.
Given the foregoing, when lining up the bunker shot it is good practice to address the sand rather than the ball itself. This ensures proper aim at the impact point. As well, it helps keep the body and shoulders lined up with the target line rather than to the left which can occur as a golfer address a ball which is forward in the stance.
When swinging, you can alter the distance of the shot by taking more or less sand. Just remember to force the swing to continue to a full finish position to ensure no deceleration occurs.