Pressing your shutter release halfway not only helps you beat shutter lag– it helps you change the mood of your picture. You can deliberately overexpose your shot to give your subject a dreamy look, or you can underexpose to get a spectacular silhouette. Click for more. You simply have to meter off the darkest (to overexpose) or brightest (to underexpose) spots in your frame, half-press, and then recompose your shot.
If you have some degree of manual control on your camera, you might see a little bar in your display, usually with gradations from -2 to +2 and a little pointer that slides left and right. This is your exposure level indicator. You can slide this left to darken your shot, and right to brighten it. You may need to consult your camera’s manual to learn how to do this.