I'm afraid that there's really no sure-fire way to make them longbeards come running. One piece of advise is this: Whatever type of calling you do, don't over-call. This is one instance where, if you think a little is good then a lot must be better, does not apply!
I agree with Simp, but sometimes the basic simple calls are the ones that work the best. Sure there are a times when fancy cuts and yelps work great, but there are more times were a simple series of yelps is all you need. I've called birds from a couple hundred yards away doing nothing but making simple clucks and purrs like a feeding hen.
Give it to them when they want it, and back off when they don't! The tough part it telling the difference....
There are cd's and tapes on the market that really help with this. Good luck!
Nothing brings them in any better than a feeder going off. Of course this is not really what you are talking about.
Try anything that you think they want to hear. If they are loud be loud then shut up. If they are soft be soft then shut up. No reason to call to much once they respond.
Remember you are reversing nature by having the gobbler come to you.