Stick with it
As you can surmise by my boardname I love to use mouthcalls for all the hunting I do - turkey, coyote, deer and waterfowl. I grew up using my natural voice to call ducks (called "yankin"), which was a practice passed on from my grandfather on down in the area I grew up (Reelfoot Lake, TN). I've always been able to blow calls well (goose, duck, tube calls, open reed and closed reed predator calls) ...... but.....
definitely, mastering a diaphram turkey call took the most time and effort. I blew them constantly for sevaral years before I thought I was really starting to get "good". It takes time. Stick with it. I had a great teacher so I knew what "good" sounded like. That helps.
Get some of Lovett Williams recordings of live turkeys and mimic them. Find a friend that is a good caller and work with him. Join the NWTF and go to you local banquet or calling contest and listen to those guys.
My preference is the cut 3-4 reed calls. Most of mine are custom these days made by people I've met over the years. I've used some of the Woodhaven calls and really like them, especially the Sadler McGraw Signature model. Also like the Southland Jim Pollard calls, batwing III, IV and Smackdown. Jim used these to win the Grand National Senior division last year.
Stick with it - It takes some time. The most important thing is open your mouth and don't choke the sound down with your hand where it sounds like you are calling from the bottom of a deep hole. Work on the rhythm of your calling.