Consider your depth of understanding and knowledge in your 
career path or academic field.
Do you feel confident about your knowledge? 
Are there particular aspects of your field about which you'd like to develop deeper understanding?

Identify your personal strengths, and leave no stone unturned: review your resume, your academic record, your extracurricular involvements.

Think about what strengths and skills you may have developed or gained from your personal life and any obstacles you've overcome in your life.

Focus some attention on your interests and what guides your choices and decisions. These values and traits are unique qualities that you will want to highlight and be aware of while you are writing and interviewing. 

Identify  your weaknesses in an honest and objective way.
Weaknesses and/or struggles are opportunities for learning and growth:
Think about strategies you may develop to improve upon current weaknesses.

Reflect upon the fit between you and your graduate school, career, and personal aspirations: Are your goals realistic and attainable?