Perhaps some recomments for german (book) readers: I've read "EJB 3.1 professionell: Grundlagen- und Expertenwissen zu Enterprise JavaBeans 3.1 - inkl. JPA 2.0 Oliver Ihns, et al"
This book is a very good one. Well, I have to admit, that I've read it twice.
Of course preparing with EPracticeLab and Enthuware is obligated :-)
And last but not least, practice coding and focus on the ascertained topic.
I've passed OCPJBCD with 93%.
What I want to recomment: When you passed the OCPJBCD, keep on preparing for OCEJPA. I you want, read "Java Persistence API 2: Hibernate, EclipseLink, OpenJPA und Erweiterungen Wehr, Harald".
Some topics of OCPJBCD and OCEJPA are the same (e.g. transaction). I have kept on preparing, it was worth and i have passed both.