This week's giveaway is in the EJB and other Java EE Technologies forum. We're giving away four copies of EJB 3 in Action and have Debu Panda, Reza Rahman, Ryan Cuprak, and Michael Remijan on-line! See this thread for details.
I think you should know things like what is in the root of a collection heirarchy. Maybe what interfaces are implemented by Maps , Sets , Lists they are straight forward. Things like what collection can hold unque values. I've seen questions on a mack exam like can they hold primitive values ? Answer no they deal with objects. So read about stuff like that. I find collections very easy topic.