Tp begin with...  Understand the javax.ejb. * API really well. You should know what each class, interface, exception does.  tags in deployment descriptor  j2ee design patterns from sun's website (atleast what functionality each pattern provides)  difference between 1.1 and 2.0
Some more to add up: 1. transaction attributes and differences between them 2. How do u deloy a bean? (explain practical steps like how do u package? where do u deploy? application server dir structure etc.) 3. How to lookup a bean and call a method on it? 4. why portableremoteobject.narrow() 5. local/remote interfaces differences 5. ejb-ref, ejb-resourceref, env-entry tags in DD 6. why no unsetsessioncontext() API? 7. ejbremove symantics for session and entity bean 8. tx attributes for message driven bean. 9. can u have an entity bean w/o ejbcreate ? why? 10. bean managed and container managed transactions I guess this shd help.