I think the best way to prepare is to study first , take mocks and do revisions.
For mocks you can refer to this site faq.
Initially before studying , I was getting 49-50% right.
After studying khalid mughal once , I took K&B book and studied that once.
In the mean time , per week , I took 2 mocks on saturdays, at times when questions per mock were less I took 4.
go through this --> http://www.javaranch.com/certfaq.jsp
Also go through the two minute drills and the rules round up game mentioned in URL above