You should focus your dissertation on a specific element that has to do with your graduate degree. For example, if your MBA has a focus in a financial area, you'll want your dissertation topic to be in the same area of study. Ideally, your dissertation should help you prepare for your future career, not just fulfill a requirement for your graduate degree.
Choose a topic that is easily researchable. You won't want to prepare your dissertation on a topic that doesn't have substantial backing. Peruse business journals to get ideas of topics that are popular. Chances are, you'll be able to find enough supporting information for your dissertation. Topics that tend to have a lot of information available include subjects relating to minority groups, teenage behavior, economic conditions, education, employee management, small businesses and retirement. You can also focus your dissertation on a specific company. Choose a large company that your professor will be familiar with, or a smaller, local company that would be of interest.
Choose a topic that is timely and relevant to current times. New information is constant, so make sure that your sources are up to date. The topic itself should be interesting to today's readers. Stay away from topics that were important in the past, but no longer are as interesting. You should be interested in your dissertation topic. You're going to be carrying out a ton of research for your dissertation, and the whole process will be easier if you're interested in and inspired by your topic of choice.
Meet with a tutor who is familiar with MBA dissertations to find out the guidelines you should follow to create the best dissertation possible. Also, hold on to all of your notes and information from your classes; these could help you formulate new ideas for your dissertation or could provide you with some sources.