My son just passed this exam. He is a high school school student without much interest in the subject going in, so he was really starting from scratch. Here is what he did:
First, he took a very basic government class. It was not nearly enough to prepare him for the CLEP, but it was his first exposure to the subject.
As part of this class, he watched the Standard Deviants American Government DVDs. Again, not enough for the exam, but made him more familiar with the subject.
Then, the test prep began in earnest. He read the Cliff's Quick Review book and the REA book.
He watched Crash Course: Us Government and Politics - 20 short, entertaining videos:
https://www.youtube.com/watch?v=lrk4oY7U...lTrqvhrz8H
He did not use the flashcards on this site. HOWEVER he did go through the member's only feedback section and studied specific topics previous test-takers mentioned.
He took lots of practice tests (REA and Petersons) and reviewed all the answers he got wrong.
Ultimately, he passed with a 63.
Now, someone who has more general knowledge of American government wouldn't need to put in as much effort as he did. But this took him from essentially zero knowledge to a decent score.
Hope this helps!