This video golf lesson features Jack Olson demonstrating a short pitch shot. According to Olson, many golfers have trouble with this type of shot, but it is not as difficult as it seems.
The movement required for this shot is basically the same movement as an underhand toss. Before making the actual shot, take a few practice swings with only your dominant arm, using the club as an extension of the arm and the clubface as the hand, and employ an underhand tossing motion.
This will allow you to get a feel for the stroke, which will give you better results with short pitch shots.