Set up the ball off the inside of your back foot. Besides the ball position, there are no necessary changes needed to the swing. Therefore, when coming down into the swing, the angle of the club will allow the ball flight to be low.
Focus on the desired ball flight and swing after addressing the ball. Visualization of a good golf swing is always a positive way to start and to execute the real swing. Then when entering your backswing, keep your hands back away from the body and come down smooth into the ball. This will help to keep from slicing or hooking the ball and will keep the swing in plane. There is no need to force this shot, just allow the clubhead to do the work.
Know that the most vital point of completing the punch shot is the follow through. When completing the punch shot, finish the swing low and towards your target. This will aid the low trajectory of the shot and help to avoid mishits. If the swing is completed properly, the ball flight will be low while not sacrificing much distance.