Here is a list of useful PostgreSQL Books. You can pick one and read it to gain more knowledge and skill to work with PostgreSQL more effectively.
Beginning Databases with PostgreSQL: From Novice to Professional, Second Edition (Beginning from Novice to Professional)
Beginning PHP and PostgreSQL 8: From Novice to Professional
PostgreSQL (2nd Edition)
PostgreSQL 9.0 High Performance
The PostgreSQL Reference Manual Volume 1: SQL Language Reference