Ha ha... The million dollar question!
Well, first of all, don't brush aside the leadership thing. A lot of people say, "Yeah, I have to show leadership in my app," and then utterly fail to do so. Did you make a difference in your workplace in your community? Because of you, did something happen that absolutely wouldn't have been accomplished if you weren't around? Or were you simply following instructions and doing a good job? The latter isn't leadership. And while adcomms would like to take you at your word when you say "I'll be a good leader once I'm given a chance to lead," they're really only going to be interested in people who sought out leadership opportunities and made things happen.
Besides that, HBS is looking for interesting people who will contribute unique points of view in the classroom. And they want people who understand the value of business school. Again, this is where applicants miss. They think, "Yeah, I need to learn finance and all of that," but HBS (like all schools) likes to think of itself as a place where people undergo life-changing transformations. And HBS wants to see why you value a general-management education, more so than a specific education in finance or marketing or whatever.
In the end, there really are magic words that will make your application a sure thing. I wish that weren't the best answer that I can give you, but it is. Good luck.
Scott
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Co-Author, Your MBA Game Plan