Just passing along that I give the Jim Evan's Maximizing Two Umpire System book positive marks.
Truly, if you read enough online and free manuals you may get some of the content of this $70 book...but to have this info on one place has already paid off as a couple of umpires I work mostly with an I are learning.
The diagrams are also very clearly written and also helpful. Again, if you do enough internet searching, you can probably find comparable diagrams as well.