What you want to do is pick and choose exactly what you want to get .  Oracle DBA certification, APP , or OCM.

Based on your goal, start there and decide what Certification PATH is right for you.

Once you decide, look at the exams that are required to meet that certification path.

Then start one by one with the exams.  Before you schedule your exam, look for prep work for each of the areas . 

You'll need to know and read up on various parts (administrations, sql pl/sql, backup/recovery, performance, etc..)

Find study guides online and/or your local book store... and then take practice exams.  Practice exams are the best ... you should try several different practice exams on the same topic you get the idea on what type of different questions they ask.

Once you have a good level of confort, then schedule the exam and good luck.

Thanks,