If you're serious about joining the military, then get serious about the Armed Services Vocational Aptitude Battery (ASVAB).
What is the ASVAB?
The ASVAB is a timed multi-aptitude test. Your scores in four critical areas -- Arithmetic Reasoning, Word Knowledge, Paragraph Comprehension and Mathematics Knowledge -- count towards your Armed Forces Qualifying Test (AFQT) score. The AFQT score determines whether you're qualified to enlist in the U.S. military.
Your scores on the ASVAB will determine how qualified you are for certain military occupational specialties and Enlistment Bonuses. A high score will improve your chances of getting the specialty/job and signing bonus you want.