Get- “St. John Off The Beaten Track” by Gerald Singer (  http://www.amazon.com/St-John-Off-Bea...  ). The book is a comprehensive resource for information about the  history and geography of St. John. This source of authentic info is well regarded by the locals and the hiking and snorkelling sections are a must for any one hoping to get the most out of their island vacation.

"St. John - Fins, feet and four wheel drive"  by Pam Gaffin ( http://www.amazon.com/St-John-Feet-Wh... ) is like having a local in your pocket. The book is chock -full tips and of details about everything you would need to know to expertly navigate your way around the island- in the water, on the trails or on one of St. John's spectacular undulating roadways.