A good score on the ASVAB is different than a minimum required score.  Each of the military branches will have their own minimum required scores (see below).  In practice, however, each branch will be more selective in their recruiting.  A score of 50 on the ASVAB implies that you scored as well or better than 50% of comparable test-takers.  Since ASVAB scores are used for many purposes (e.g., enlistment eligibility, military job placements, and career exploration), it is important that you score well on the ASVAB.  A score of 60 or better should be your minimum target.
Many high schools give students the opportunity to take the ASVAB as part of career exploration. If you chose not to take one in high school, then you will have to schedule a time to take it. You can contact the Armed Forces Recruiting Officer in your area and you can schedule an appointment with a local recruiter from the branch of the military you wish to join.
There are essentially two options when it comes to preparing for this test. First, a person can attempt to reassess all of the information that they learned over a decade by spending hours compiling information. Secondly, a person can find a specially formatted ASVAB practice test that covers all areas of both the written test and computerized test. Clearly, the best choice is the ASVAB practice test. The question becomes “Where does one find an accurate ASVAB practice test?”
After adding so much information to the aptitude test, there was a bit of difficulty interpreting the test results. In addition to that, a vast majority of test takers were deemed as being under qualified based on their test results. This is why the percentile change was made. It ensured that a 50% actually correlated with a person doing better than 50% of the test takers. Those revisions have worked hand-in-hand with the preparation of the armed forces.