Allright man, you gotta do TWO things here:
1. Start volunteering somewhere - Start as quick as you can, and try choose something that excites you, something that will give you opportunities to lead. This'll help you out a lot.
2. When you write your essays, do whatever you can to "break the mold" of the "accountant". They aren't gonna like it if you were just a number cruncher, but they want to see initiative, leadership,.. basically they want to see that you got out there and did business!
Other than that, assuming that you don't have any additional leadership experience, I'd say your sweet spot is the top 20 outside of the big three S/W/H. Doesn't mean that they are impossible, and a lot can happen between now and then, but when building your strategy, make sure you get a nice mix of schools in there.
So start looking at the top 20, see which ones appeal to you in terms of location and program, and if you got anything else, you just come back and chat with us.