I'm probably the last person to give advice but I still wanted to share my experience as I just sent in my application to B-school. Gulp.
I started almost three months ago drafting my Essays with the help of Bodine's Great Applications to Business School, which has some great pointers but the essays were very long (I wished I had that much room to blather on) and not very relatable (some pretty heavy on the sob-story; I refuse to go there even if I did have a rough childhood
. BTW, does that even work?). The pointers alone are worth getting the book though. Following Bodine's book, I sat down and took inventory of my life and that helped get the ball rolling.
Then I would set them aside for a month or so, revise them and set them aside again. What I noticed with my essays was how much they changed from the first draft and sometimes second and third drafts. I'm not talking about grammatical changes but serious content changes. I would read an article that made me recall an experience that should be highlighted or I discovered more reasons for an MBA. I even flip-flopped between doing the optional essay or not. Then when I decided to do it, the topics changed frequently.
Bottom line, I knew they were challenging by the fact that I kept avoiding a final draft, but don't end up like me where you are polishing them on the day of the deadline. Give yourself plenty of time and have as many people review them and provide pointers. I had a team of three reviewers. One checked grammar and flow, another provider a different approach, and the other read it from an adcom's perspective.
Don't worry about changing your story. Constantly think about the program you are interested and how you fit into that program. Essays are not easy and can make or break you. Maybe that is old news. BTW, I saved essay 1 to do last because it is the most important one and sets the tone for the other essays. What?! Yep, I am backwards.
Maybe that was totally useless info. My brain is spent.