To start, you could be using the wrong mouth call. Every mouth call works different because of the thickness of the latex and the number of reeds in the call. The easyest to start with is a double reed call. Don't start with a single or multi reeds more then two and with no cuts in the reeds at all. Clear calls are best...

The tape can be cut off a little at the time, but do not bend the frame. If the frame is to large drop down in size. I call off the frame only so there is not such thing as cutting to much off.

Place the call half way back on your tongue and place it up in your palete. First take a breath of air and as you apply presure up with your tongue say SHHHHHHHHHHHHHHHH , you should get a high pitch. If not apply more presure with your tonge and do the step over until so.

Once you get the high note hold it as long as you can and take only enough presure off to hear the note drop in pitch. Once you hear the change in the note, put the the presure back up to the high note. Do this over and over faster and faster until both notes come together and create the yelp....

Hope that helps...