You have asked a very good question which many others will never ask! Because they will never know what they are doing.
MBA is essentially a Master Digree where your Field experience will count. The examinations are of different pattern, not like your earlier accademics. In your earlier examination you might have written answers to questions by selecting most of the lines from your text book (By-Heart sometime!!), which will be purely theoretical. But here you will be asked to solve practical problems. You will have to answer by framing your own sentences and views. You need to refer to various 'reference books' along with your usual text books. If you have already experience in the respective field it will be easy to understand the concepts and solve the problems very easily sometimes even without reading books! If you are keen on doing MBA My suggestion is, keep reading business news papers and magazines. These are very essentials for knowing whats' going on presently throughout the world. I have 15 years of industrial experience with BE Mech and Final MBA now.My advice join to a properly organized company, stay for 2 years, then join MBA. All the best.