I highly recommend the vanguard book, Design Patterns, by the Gang of Four (Gamma, Helm, Johnson, and Vlissides). In addition, I would read some Java publications, such as Java Pro and Java Developers Journal. Incidentally, Java Pro has a column written by the author of Java Design Patterns, James Cooper. Also, I have read articles in the Java Report written by Vlissides and read articles in Java Developers journal by the others of the J2EE patterns book.
As for a strategy for learning patterns, if possible, I would try to find a mentor who knows what they are talking about and learn as much as possible from them. Study groups is a great idea too!