Declarations and scoping 91%
Flow control 90%
OO concepts 80%
Collections and Generics 80%
In addition to usual advice of reading the book -- I used Bates & Sierra and recommend it highly -- and writing a lot of code I also recommend the following:
Get yourself a whole bunch of 3x5 cards and, each time the book relates any testable fact, or whenever you get something wrong on a practice exam, write it down in the form of a true/false question, fill in the blank, or whatever format seems appropriate, and write the answer or explanation on the back, with the page number it can be found on. This newbie, not having a lot of experience to help him remember stuff, found this technique helpful (and cheap). You can go over your index cards on the train, etc.