There are a lot of good points in my colleague Ann Levine's book The Law School Admission Game: Play Like An Expert. In particular, I want to point out her advice regarding avoiding pleas for acceptance. I notice many applicants make this error at the end of personal statements for medical school, residency and fellowship. Here's Ann's take, which I think is very useful:
"Your personal statement should convince the reader to admit you based on the strength of your experiences and perspective. No begging at the end. None of this, "I truly hope for the opportunity to prove myself" nonsense..." (p.91).
Remember: If you make yourself a distinctive candidate through your accomplishments, you won't feel the need to address your reader in this manner.