I'd say the best way to start is to start studying. Here are two books you're going to need:
Here are the latest editions of the SCJA books:
SCJA Study Guide by Cameron McKenzie
SCJA Questions Guide by Cameron McKenzie
I wrote them, so I'm biased. Robert, who posts here, wrote an excellent book as well.
Ask lots of questions, do lots of studying, and when you're ready, schedule the exam. That's how it usually works.
Good luck!
-Cameron McKenzie