This is an excerpt from Basketball Shooting by Dave Hopla.
When shooting, you build the shot from the ground up, just like building a house. In this case, the foot position for shooting the ball is your foundation and should be the same for all shots, whether shooting a jumper or a free shot or shooting from beyond the three-point line. Consistency leads to greatness and consistency starts with the feet.
To begin, start with your feet together (see figure 3.1a) and slide the foot opposite the shooting side, for a right-handed shooter this is the left foot, back until the toes are even with the arch of the shooting foot (see figure 3.1b). Then, space the feet so that they are shoulder-width apart (see figure 3.1c). This will ensure that the base isn't too narrow or too wide. If you have a narrow base, you will have poor balance and it will hinder the range of your shot (see figure 3.2a). If your base is too wide, you won't have the quickness or explosiveness necessary to get your shot off successfully (see figure 3.2b). In this stance, the lead foot, or shooting foot, is the foot on the same side that you shoot the ball with. For a right-handed shooter, this is the right foot. The toes of the lead foot point toward the target. This positioning creates the shot line, in which the toe, knee, hip, elbow, shoulder, wrist, and basketball are situated as close to a straight line as possible in relation to the target (see figure 3.3). Maintaining this line will increase your shooting percentage and eliminate unnecessary movements throughout your shooting motion. This is the stance you should assume for all of your shots.
Once the feet are shoulder-width apart and positioned properly, you must ensure that your knees are bent so that you have better balance, more power, and more explosiveness in the shot. When you bend your knees, you should also bend slightly at the hips, bringing your head down so that the shoulders are positioned in front of the feet and the head in front of the shoulders (see figure 3.4). If you just bend at the knees and don't bring the head and shoulders forward, your heels will stay on the floor, forcing you off balance when you catch the ball and start your shooting motion.
Many shooters will bend at the knees but fail to bend at the hips, making the body too upright and leaving the heels nailed to the floor. To practice bending at the hips, lean forward and attempt to get as close to the basket as you can without moving the feet. To do this, you will naturally be forced to bend at the hips. Hold this position for a few seconds and repeat several times to become familiar with how the positioning feels.