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.
You already know that your personal statement could be the one factor that keeps you out, or lets you into the school of your dreams, but you may not know how important it is to have a fresh set of eyes on it before you turn it in. While you may have read over your personal statement several times, there are still reasons that you will want someone else to read it over as well.