I bought a diaphragm(mouth) call that had a instructional CD with it, I took it in my truck and played it and used the call to practice with the dvd. I know people thought I was nuts while driving down the road making all of these crazy sounds but I practiced for a long time until it was time to go hunt this last spring and I did manage to call in 2 toms. One of which my BIL took and the other didn't commit fully so no shot at that cagey old bird. Like was previously said, practice will be your best friend and the birds will dictate what sounds are good and which are not. Good luck in the upcoming season.
Born to hunt and fish.