(Manager, Business Operations, Elegrity, Inc.)
The answer depends on several factors, including what course of study you are pursuing. Some programs, for example in operations and accounting, may require fairly recent coursework in the subject, or you'll have to re-take the courses or test out of them. The period is usually within 5 years, so I believe getting 2 or 3 years of work experience in your desired field, or at least a related field, will provide a student the best value for money in pursuing the MBA. A very good consideration is to work several years and then attend a fully-accredited evening MBA program, so you can work while going to school (helps with financing it, too.) In this way, you'll be able to apply real-life experiences to case studies and also potentially use work situations for class projects. If you have been out of school for many years, the 'executive MBA' may be an option, although many business recruiters and HR departments will look at an executive MBA as kind of an 'MBA-light,' especially if these are granted from a second- or third-tier institution.
The MBA is only as good as the school granting it, so I would strongly recommend that you select a fully accredited and nationally recognized MBA program, otherwise you may not get the return that you had hoped on your investment in the degree. I would also avoid online MBA programs, as in-class discussion and group project work are very important for the education value of the degree, and also for networking opportunities.