If you have a lot of wind or have branches blocking your normal ball flight, you need to hit the ball low. The keys to this shot are: de-loft the club by placing the ball back in stance, placing 60% of your weight on your left leg (for a right handed player) and have an abbreviated finish. Take a look at these two videos that show you two ways to do it: video 1 and video 2.
The second video is from Justin Rose, the 2013 US Open Champion. Congratulations to Justin on his great win !