The Preface contains a section called Other Resources which might help. Basically it says that having the specs. and API docs on hand can sometimes be useful - especially if you think of a question which you can't find the answer to in the book. Other than those, I would always recommend making your own condensed notes of things you can't remember, and always doing some practical work, building and deploying components. I find I learn a lot more when things go wrong and I need to debug them compared to when they go right (learning from my mistakes). Don't be afraid to make plenty of mistakes - this way you'll end up asking yourself more questions which will only act to help you understand things better!
Charles Lyons (SCJP 1.4, April 2003; SCJP 5, Dec 2006; SCWCD 1.4b, April 2004)
Author of OCEJWCD Study Companion for Oracle Exam 1Z0-899 (ISBN 0955160340 / AmazonAmazon UK )