Focus on the head. Specifically on the white chinstrap.

The human eye has a tendency to key in on things that move....on a goose...that would be the feet and the tail. Think of that white chin strap as a clay bird, and you'll bust them every time. Geese are some of the easiest birds to hit. They are deceptively slow...but as long as you swing out in front of the head, and not the body....no problem.