Hello Ermias,
Most people I know prepare by taking as many practice quizzes/exams as possible. They use the results of each to direct their studies in either the PMBOK guide, lecture/video material, or both to improve their understanding of the material. How you best study for the CAPM exam is certainly up to you, but I found the PM PrepCast material invaluable in my preparation and success for passing the CAPM exam, on my first attempt.
Best wishes on your studies and CAPM exam.
Respectfully,
Coy