Often, people will ask about allowing their birds to perch on their shoulders. Most birds will begin to exhibit problem behaviors, especially aggression during breeding season, if we allow their heads to be higher than our hearts. Unfortunately, birds enjoy being up higher, and keeping them off of shoulders can be difficult. If the bird is kept on a perch of the proper height, it will begin to relate to you at that level at all times, and it will be less obsessed with sitting on your shoulder.
As with any other behavior, be clear with your intentions when training your bird to stay off of your shoulder. This can be done by giving it only two options. One option is to sit on your hand or arm like a little lady or gentleman. The bird's other option is to go back to its cage or perch for two to five minutes. If no other options are offered, the bird will eventually accept sitting at the lower level.