Some time ago I got first the Oracle Certified Associate certification and later the Oracle Certified Professional certification, both on Oracle Database 10g. Since then there has been some people asking me about the procedure I followed and also the study material I used to prepare this tests, and it's until today I decided to write about it.
First of all, the tests are multiple-choice question exams that are difficult enought to not let to pass anybody that can pay the exam fees (I think low by the way), and not being a native English speaker adds a lot more complexity to the tests. If you have experience managing Oracle databases AND have a good and fresh knowledge of Oracle Database concepts you will have a good chance to pass the tests; in this kind of tests it is very important to have rock-solid concepts knowledge because all answers looks equal and the subtle differences are the key to choose the correct answer, not to mention the limited amount of time to answer the whole test. Oh, did I stress having good English skills?
On the other hand, if you're on budget you will find that a thorough study of the official (and free) Oracle documentation may be enough to pass this tests, and even the Express Edition (free) is enough to practice in your own computer. But if you can spare some money, I highly recommend to buy the SelfTest's Oracle Database 11g: SQL Fundamentals I, Oracle Database 10g: Administration I and Oracle Database 10g: Administration II practice tests; the price of this software is close to the price of each certification test but it might save you frustration and time, not to mention money, therefore is up to you to prepare for this tests just with free documentation (or expensive courses) or pay the extra money to practice tests with this software. If you buy this software be sure to score at least 90% a few times and you will have a good opportunity to pass the real tests.
But if you're a cheapskate like me you would prefer to study the official Oracle documentation. To be honest, at this time I can't remember exactly what I had to study for each certification test, but if you are willing to hold the OCP certification simply study all the following guides and you will be safe.
For the SQL test (Oracle Database 11g: SQL Fundamentals I, 1Z0-051):
Oracle Database 2 Day DBA
Oracle Database Express Edition 2 Day Developer Guide
For the OCA certification (Oracle Database 10g: Administration I, 1Z0-042):
Oracle Database Administrator's Guide (chapters 1 to 20)
Oracle Database Backup and Recovery Basics
For the OCP certification (Oracle Database 10g: Administration II, 1Z0-043):
Oracle Database Administrator's Guide (chapters 21 to 28)
Oracle Database Backup and Recovery Advanced User's Guide
The problem of studying Oracle documentation is that it is not intended to be a self-learning guide, therefore you have to figure out exercises to practice what you read; just reading this documentation without practice nor experience will not be enough to pass the tests. But in my personal experience I think these guides are so well written that if you manage to learn them you will not have any need to buy (or read) other books; in fact I cannot recommend books because I didn't read anything besides the Oracle guides to prepare for the certification tests.
Another problem is that these guides are good for preparing the OCP and OCA tests, but for the SQL Fundamentals test I couldn't find one Oracle guide that covered everything; in fact I was very close to fail that test but the SelfTest software saved me. On the other hand, the OCA test was difficult to me but it was less than the SQL test, and the OCP test was the easiest one to me. Therefore, if you're more a DBA than a developer it would be better to study SQL sentences and functions a lot.
Now let's talk about the certification track and prerequisites. If you're pursuing the OCP or OCA certifications you first have to pass one of the SQL tests, more likely the Oracle Database 11g: SQL Fundamentals I. You can take the OCA or OCP tests first but you won't get any certification unless you clear all the certification prerequisites, therefore first try to pass the SQL test.
If you manage to pass the SQL test then you can take the Oracle Database 10g: Administration I test, and if you pass you will hold the OCA certification. Easy, isn't it?
But this is just the beginning, the goal should be the OCP certification but there are two prerequisites not so easy to cover: take an approved course and fill the Course Submission Form. The difficult part of taking an approved course is just paying for it, and if your course diploma has a course serial number and you took that course recently you will have no problem at all filling the Course Submission Form.
At of this writing, the submission of the form and the scheduling of tests should be done at the Pearson Vue site, and unfortunately I cannot remember what I have done exactly but you would get help at the moment of contacting a testing center.
Finally, if you cleared all the prerequisites and manage to pass the Oracle Database 10g: Administration II test, you will become an Oracle Certified Professional and get a nice plastic card just in case you are willing to boast about it.
There are people that put in question the value of this kind of certifications, but the truth is that I learned a lot studying for the certification tests, and because these certifications are valid worldwide they are a good point of reference for recruiters looking for talent. Therefore, if you have already took an Oracle approved course then put a little effort and money and go for the OCA and OCP certifications, I think they have good value for the money.