Avoid a catalog of achievements. This is only a list of what you have done, and tells nothing about you as a person. Normally, the statement is far more than a resume. Avoid lecturing the reader. Any graduate admissions committee member knows that and is not trying to learn about the field from the applicant.
Some statements do ask applicants about their understanding of the field.
Write directly and in a straightforward manner that tells about your experience and what it means to you. This is not a research paper for a professor. It should form conclusions that explain the value and meaning of your experience, such as what you learned about yourself and your field, your future goals, and your career plans. Draw your conclusions from the evidence your life provides. It should be specific.