The basic call on a short reed is to mouth the word Too-whitt into the call. Emphasize the whitt. You can draw out the tooooo and shorten the whitt for a hail call or double up on the whitt to double cluck. You can change the tone somewhat using your hand to control air flow but I think its important to have a call with good tone to begin with. What works for me is to call sparingly when the geese are at a distance then increase the frequency and urgency of the calls as the geese get closer. If you watch real geese react to a flock coming in, they get very vocal just before the new flock hits the ground.
try dropping your jaw as you blow your call,this will stop you from puffing your cheeks out.your supposed to bring up the air from your diafram rather then puffing your cheeks.......fowl