Okay, if you have strong confidence in your past performance, you need to present to the school your abilities evidenced by tangible supports ( for example, a recommendation letter containing comments by your immediate boss), and any seen improvement in your performance over the past working history, and your potentials and special interest in a certain field which you are seeking for or switching to with a help of an MBA degree from a top US's universities. I think whatever your current working background is, the essential successful element is a clear opinion and judgement on yourself over why you want to pursue an MBA? why an MBA in your selected field, and why you can be chosen by the school from the common pool of candidates? All these your opinions and judgement should be "perfectly" reflected in the essays to be reviewed and commented by the admission committee. | 
