This is a tip that helped me. Set up a fairly large target with a crosshair drawn form top to bottom and side to side. With the gun empty, focus on the front sight and aim at the center of the crosshair. Press the trigger in one steady pull. At the second the hammer falls, observe the position of the front sight: high, low, left or right of center. Right or left of the crosshair can be caused by finger pressure to the side of the trigger or the thumb pushing against the side of the pistol. Above or below the crosshair is caused by jerking or anticipation of the hammer fall.