Research which specialization areas are offered by the schools to which you intend to apply. There are many concentrations available to MBA students, but not all schools offer all areas. Browse each school's website or contact the admissions office to determine what your prospective institutions offer.
Consider your prior education and past employment experience. If you received a bachelor's degree in criminal justice or worked for a law enforcement agency, perhaps the specialization area of criminal justice administration would be the ideal stepping stone to advancement within your current place of employment. Even with an MBA, employers are likely to want prior relevant work experience and education when comparing applicants. Focusing on a specialization area in which you already have knowledge can place you ahead of the competition.
Evaluate the job market. It's hard to predict which markets will be experiencing job growth in the one, two or more years that it may take you to earn your MBA. Regardless, read business magazines to stay on top of employment growth predictions, and select a specialization area that will meet the future demand for skilled and knowledgeable employees.
Pursue something you'll enjoy. While employment prospects are important, you will be spending several years and possibly a significant amount of money to earn an MBA, and you will need to be prepared to work in the area of your specialization for years. To get the most out of your investment, select a specialization area that truly excites you.