The MPRE is straight black letter law. I probably overstudied, but I passed the first time.
Don't take this test too lightly, however, because I know a couple of people who had to take it more than once.
If you had a rule based PR professor (like I did), I would recommend reading over the barbri long outline a couple of times, and taking all of the practice questions in the back of the book. Also, make sure you review ALL of your answers, making sure you got questions right for the right reasons, and knowing why you got specific questions wrong.
I studied for this exam on my lunch breaks during my second year second summer job. I walked out feeling like I failed, because the questions are tricky (not MBE tricky, but still, sometimes had to guess between 2 answers). If you read the barbri outline and work all of the practice questions, you should be in good shape.
My friends that didn't have a rule based professor for PR also used the PR flashcards in the yellow box. This gave them rules and hypos. But be careful with the flashcards--some of the rules have changed slightly since they were printed. Other than that, a good resource (if you are somewhat familiar with the rules you will be able to spot the inaccurate cards, they are pretty obvious.)