As we make our approach to the field we slowly reduce power to maintain a slow descent keeping our eyes on the spot we want to touch down on. To accomplish this let's imagine a small box around that spot. If as we descend the spot appears to be rising in our box we are descending to fast and we need to increase the throttle slightly. Likewise if the spot seems to be moving downward in our imaginary box then we are not descending fast enough and we need to reduce the throttle slightly. This will keep us on the proper glide path for a good landing. Pretty simple, huh?