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.
It is important to put yourself in the shoes of the Admissions Officer: why would your personal statement be unique, how are you different from the other candidates? Primarily you need to decide how you will divide your personal statement into digestible chucks. The most obvious way is to divide into paragraphs of 100 words. If you aim for between 500 and 600 words at most, it will help your admission officer when they have to read thousands of personal statements to find the perfect student.