I would read all I could about the history of the persons, places and events surrounding the particular cache you're going after. Local history, lore, etc.
For general cache hunting, Karl Von Mueller is a good read, but honestly, you can probably learn as much here on this forum as you can from books.
Though there are many books on cache hunting/treasure hunting in general,Two that are defiantly worth looking into are the books "Treasure Hunters Manual" by Karl Von Mueller. as well as the book "Search" by James R Warnke.