After grammar and spelling, the next problem that needs be checked is transition. Read your essay. Go through it from end to end, and check to see if your essay flows smoothly. Does each sentence flow smoothly to the next? Does each paragraph flow logically to the next? Each statement should be connected or somehow related to the one before it, not thrown randomly together. Next, limit the use of "I" in the beginning of most sentences as it is already obvious that the essay is a piece written by an individual.
In talking to Admissions Representatives across the country, there is one aspect of a personal statement they all agree on _ BE YOURSELF and let them get a feel for the type of person you really are. This includes your motivations and the ability to evaluate your personal experiences and the effect they had on you. If you can understand that 8 out of 10 personal statements fail to do this, then you are well on your way to being 1 of the 2 applicants in every 10 that stands out.