Before making a pitch you must evaluate and decide what type of trajectory you are attempting to impart upon the ball. Once this has been determined you must first select the correct club from your bag (most often one of the wedges), and second, you must determine where to place the ball in your stance.
The further forward you move the ball in your stance (i.e. toward your target) the higher the resulting trajectory will be. The further back you move the ball the lower the trajectory. This allows you to hit a multiple of different trajectory shots with the same club. It is important to note that the trajectory that the ball takes to arrive at a certain location will, in concert with other factors, determine the amount of additional forward roll you will get on any particular shot. As a rule, a shot with a lower trajectory will result in more forward roll than will a shot with a high trajectory.
Only through practice will you be able to determine which club, in combination with which ball position, results in any given trajectory. Once practiced you can bring your new found knowledge onto the course and lower your scores with shots that get you closer to the hole because you can land the ball where you want to and with the appropriate momentum.