The first step to making authentic sounding turkey calls is knowing what real turkeys sound like. To learn that get a CD of real turkey talk usually available at hunting supply stores or on the web. These are good ones http://www.lovettwilliams.com/prod_cass_all.html
Or you can download some recordings of real turkeys from the web. The NWTF web site has sound files of the various turkey vocalisations. http://www.nwtf.org/all_about_turkeys/calling_tips.html
So does this site http://wildturkeyzone.com/hunting/calldescriptions.htm
A young child is nearly fluent in his mother tongue before he goes to kindergarten. He accomplishes this by simply hearing the language day in day out without formal training. Similarly, you can start to learn the language of the wild turkey by hearing it often. Listen to a CD while driving or as background at home when doing chores.
Actively listen for the rhythm or cadence and the various inflections and feelings turkeys put into their calls when they are excited. By hearing their language repeatedly you will automatically know when you own calls sound right when you start to make them.
If you are new to calling do a serious amount of listening to turkey calls before you pick up your calls. If you have been calling for a while, listening to real calls will keep you sounding authentic. You might even have to change your calling to match up with the real deal.