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.
The person you choose to look over your statement should be checking everything. Along with grammar and spelling errors they should check the tone of the paper, the flow of the paper, and the overall style of the paper. So, it makes sense that the person you choose to look over your admission essay should be well tuned in writing. Additionally, they should also be able to let you know if there is anything they feel you should omit or add. Once you have made the changes they recommend, then you should have them re_read your personal statement to ensure quality. If you want to be ultra_safe, then have yet another set of fresh eyeballs look over your revised personal statement.