Depending on your background, I would suggest:
1) Read book: OCA/OCP Java SE 7 Programmer I & II Study Guide by Kathy Sierra and Bert Bates (possibly twice if you have to)
2) Create your own mini Java programs to understand the concepts in the book
3) Do plenty of mock exam questions, both the ones in the above book and the others available on the net (see also
SCJP FAQs on this site)
Good luck.
SCJP 1.4, SCWCD 1.4, SCBCD 1.3, SCJD, SCEA/OCMJEA
Live life to an interface, not an implementation!