An integral part of your application is the personal statement which answers the all-important question: "Why should you admit me?" In this piece of self-promotion, you're expected to discuss your background, qualifications, and motivations for attending graduate school. This is an incredibly important part of the application and it requires careful planning. The personal statement, along with your writing sample (if required), is what sets you apart after passing the generic screening for GRE scores, GPA, and undergraduate major. In my experience, the strongest personal statements provides answers to the following questions.
Why Are You Interested In Your Field of Choice?
Demonstrate that you're passionate about your field. Cite evidence to demonstrate your interest, such as personal convictions or circumstances, coursework, professional experience, and other relevant factors. Show that you've started to explore and think about the field seriously. The reader should walk away thinking: "This person is deeply committed to this field. No doubt about it."
Why Do You Want To Go To Grad School?
Explain why you want to attend graduate school, and why it makes sense now. Perhaps you want to go deeper in your undergraduate field. Or perhaps you want to start a career where a graduate degree is a distinguishing quality or requirement, such as journalism or academia. The reasons that motivate applicants are as varied as their backgrounds, so there isn't a cookie cutter answer.
What Will You Research In Your Thesis or Dissertation?
Provide a preliminary indication of what you'd like to research in your area of specialization. For example, if you're applying to a Master's in Classics, you could propose examining the treatment of life, death, and the afterlife in Homeric epic. Schools won't hold you to accountable for what you write; they're looking for evidence that you've started to (seriously) think about the field.
What are Your Academic, Professional, and Other Accomplishments?
Delineate your qualifications for undertaking an advanced degree. Reference examples from your academic, professional, and personal life, and how each has prepared you for the depth and rigor of graduate studies. If you're applying for doctorate programs, cite evidence of your ability to teach and educate. If you've done something unique or impressive, discuss it. This isn't the time to be modest. Remember, most schools don't ask for your CV, so this is your only chance to discuss your accomplishments.
Why Do You Want To Study at Our University?
Schools want to know that you have very specific reasons for applying to their program. Some potential reasons include: the program's curriculum, the department's research focus, specific professors that you want to work with, as well as facilities, resources, or activities that are unique to that institution.
(Optional) Why Did You Do So Badly In...?
It's best not to dwell on weaknesses in the personal statement -- unless they're glaring. For example, if your grades were extremely poor (such as receiving an "F" in a class), or you have many "W"s on your transcript from withdrawing from classes, or you dropped out of school, it may be opportune to insert an apology – a couple of sentences explaining what happened. Perhaps you spread yourself too thin, switched majors, or faced problems in your family life. But only include an explanation if there's a serious shortcoming in your application.