Practice exams are hugely important for success on the bar exam, and particularly the MBE.
It is imperative that you get used to answering hundreds of MBE questions before you sit for the real thing.
You should start taking MBE practice exams early and often. But taking the exams isn't enough - the most important part is to learn from your score, no matter how bad it may be. Reviewing your answers, especially incorrect answers, is critical to learning material and understanding what trips you up.
Closely examine your score, breaking it down by subject and topic areas within subjects, if possible. Identify any patterns, particularly areas of weakness, and consider readjusting your studying accordingly. Also, pay attention to streaks of wrong answers.
As you move ahead in the study process, don't stop taking shorter, timed MBE sections, even in single subjects where you need work. Also, work on taking shorter, one-hour simulated exam sessions at least once every other day, paying particular attention to timing. The goal with practice exams is that you should walk into the real MBE feeling like you've done this a million times before.
Most importantly, don’t panic about bad scores. A freakout won’t really do anything to help you. Instead of getting overwhelmed, get focused on what you need to work on. For those studying for the July bar exam, even with less than a month remaining, you have plenty of time to strengthen areas of weakness and get up to speed.
Good luck as you enter the home stretch, and keep up the hard work!