I got this question from two new clients this week and thought I would post my thoughts here for everyone.
How much does your profile and application need to change this year if you got rejected when you applied last year?
Your story: Unless the story did not make sense or had large holes, I would not recommend changing your overall story. If it seemed weak in some areas (i.e. you are making a dramatic career switch without a lot of evidence you can accomplish this), do things that will get you closer to your new career. This could be a side project, research or volunteer work.
Your LORs: are you confident you had the best letters? If you are not sure, have a conversation with your recommenders from last year and get a sense of their interest and excitement. If your LOR isn't perfect, find someone new to write it this year.
Work: While it is getting late to make job changes for this year (though a bit more time if you are applying round two), you can certainly try to do different things at work such as get on a new project or take on a new responsibility. Evaluate your experience and see where you might be lacking relative to peers.
Extra-curriculars: While you probably had some, were they strong enough? Did they make sense with your overall profile?
Interview: If you got a lot of interviews but didn't get in, its time to hone your interview skills of course. Whether its with me or someone else, you should definitely ensure you have proper training and practice so you can ace the interviews once you get the invites.
Good luck and contact me if you would like a ding analysis or help applying this year: http://www.personalmbacoach.com/#!contact/c17jp