I use these guys. They will guide you through the process, 
http://usafarmlabor.com/
Take a bunch of paperwork and a good deal of time to get labor. This year was my first year with a H2A. I started the process February 15th and got a worker May 2nd. If I would not have paid a emergency fee the process would have taken another month.
My South African worker has been excellent. 
If you have any specific question I'll answer what I can.