First, review your notes and textbooks from your CNA program. Go over each area of basic skills, patient care, safety, and ethics as well as rehearse every skill.
Take all the practice tests. Whenever you make a mistake, revisit your textbook. Then retake the tests to make sure you have "filled in the blanks" in your knowledge of the material.
Check your Challenge Bank regularly. It accumulates all the questions that you answer incorrectly. When you answer one of those questions correctly, the question will disappear from the Challenge Bank. Study and practice to empty your Challenge Bank of missed questions.
Make sure you read the practice test questions carefully and understand what they mean. When you take a lot of practice tests, you start to expect some questions about certain things, but don't let that catch you off guard!