Senators Boxer and Hutchison were on CNN this weekend for a discussion on taxes. Each of them wore a blouse with a jacket over it, but with two different techniques for complimenting face shape using "balance points." Look at http://youtu.be/9-CNkHlXlCg (you can see both of them on screen at about 2:15):
Senator Boxer's neckline compliments balance point 1: the distance from the top of her face (below her bangs) to her chin is equal to the distance from her chin to the neckline of her blouse. The oval shape of her face is perfectly echoed in her clothes.
Senator Hutchison has highlighted balance point 2: the distance and shape from the widest point of her face to her chin is the same as from the top of her shoulder to the neckline of her blouse. Her rectangular face shape is in harmony with her high rectangular blouse.
Either technique can work for you, no matter what your face shape. You can even combine them, hitting one balance point with your neckline and the other with a necklace. Jewelry also works well if your first balance point is lower on your chest than you would like your neckline to be.