Passed with a 57, and I was sweating bullets through the whole exam because I did NOT feel confident. How I prepped:

Modern States Lectures
Official CLEP Practice Test
Peterson Practice Test
This Quizlet

I did no reading. I do not suggest this. What ultimately put me in a position to pass even without reading was that many of the questions had multiple choice answers that came from distinct time periods, so I was able to use context clues to place the subject of the question within the correct period.

Modern States lectures, Quizlet, and these 2 practice tests are definitely adequate to pass if you're a good test taker, but if you have time, I would definitely recommend at least skimming some reading resources in the areas you feel weaker. Lots of names and dates to remember.