Everyone has given great advice! The one key I agree whole heartedly with is to "push" or "huff" air across the reeds with your diaphragm. "Blowing" the call is completely mis-stated. Hence the diaphragm call.
Once you are able to start making sounds with call, I would obtain a copy of Tree Top Turkeys(treetopturkeys.com) There are two volumes of nothing but digital recordings of turkeys in the wild. Yelping, cutting, clucking, cackling, purring etc. Most every sound a turkey hunter needs to be successful in the spring woods. It will take hours and hours of practice to become proficient on your calls, but remember tone is not nearly as vital as rhythm. All hens have different voices just as humans. Ensure that you can consistently reproduce the sounds needed when hunting situation calls for it.
Below is a link to a filmed hunt of an Osceola I bagged on public land in "09". Notice the sequences of calling. I changed calling strategies as we changed set ups. Take note of the final set up that harvested the bird. The calling was dialed down to simply clucking purring and soft yelping. Hopefully this helps.