I passed the OCA 8 exam about two months ago with 92%.
I used the OCA: Oracle Certified Associate Java SE 8 Programmer I Study Guide: Exam 1Z0-808 by Jeanne Boyarsky & Scott Selikoff. While studying I did not use an IDE. While reading the book I tried to write example code to test each thing I learned. I also tried to always ask "what happens when I change this?" to learn some of the edge cases. I wrote a summary of all the things that where new to me.
After I completed the book I used the Enthuware mock exams to prepare myself for the test. I read my summary before take each mock exam. I scored pretty bad on the first one, I knew I had to learn and practice a bit more. On the later mock exams I was scoring around 80% then I took the real exam and scored 92%.
I would recommend using the book and the Enthuware mock exams both helped me a lot in preparing for the exam. In total it took me about 2 - 3 months.