I use CD's of real tueky voices.......
1. NWTF - a very good recording of all turkey sounds of spring both hen and tom
2. Lovett Williams - has instrucitonal tapes and CDs of real voice of turkeys and gives you a very good description of what the call is and what to use.

From those - I listen too each time int he truck and practice while palying so I sound just like them.

3. Expereince and being able to mimic what you hear out in the turkey woods.

JW