Give the reader, in the form of a coherent narrative, details about your academic and professional background as well as notable accomplishments that demonstrate your preparation for the degree you seek. Remember, your statement is very much akin to an academic essay: It has a thesis (I’m suited for your graduate program) that must be argued with evidence. You will need to describe the skills you have learned from academic, lab, research, or work experiences. It’s essential to give specific examples and illustrate the points you are making. The adage applies here: Show, don’t tell.

Robert Furno, the Dean of Admissions at the Graduate School of Arts and Sciences, likens a successful personal statement to a cocktail:

“It’s one part ‘what led you to where you’ve gotten,’ and two parts ‘what you want to do when you get here.’ The best essays that we’ve received are those that can articulate what brought them to this stage.”

Personal details should only appear to the extent that they explain something essential about your interests in the field or relate to your experiences. Remember this is a professional, not personal, statement

Here’s an example easily found online and in a book about writing personal statements. from: https://owl.purdue.edu/owl/job_search_writing/preparing_an_application/writing_the_personal_statement/examples.html

“My interest in science dates back to my years in high school, where I excelled in physics, chemistry, and math. When I was a senior, I took a first-year calculus course at a local college (such an advanced-level class was not available in high school) and earned an A. It seemed only logical that I pursue a career in electrical engineering.

 When I began my undergraduate career, I had the opportunity to be exposed to the full range of engineering courses, all of which tended to reinforce and solidify my intense interest in engineering. I’ve also had the opportunity to study a number of subjects in the humanities and they have been both enjoyable and enlightening, providing me with a new and different perspective on the world in which we live.”

This is awful. Don’t do this. First, reaching back to high school is an absolute no, and “seemed only logical” is a pathetically passive description of how this student chose her major. We have no sense of her real interest in science; there’s nothing special here. She was interested in engineering and took courses in engineering. That’s all we learn. The language here is also dull. “Enjoyable and enlightening?” Bland dreck. 

Another example begins just as badly.from https://owl.purdue.edu/owl/job_search_writing/preparing_an_application/writing_the_personal_statement/examples.html

“Having majored in literary studies (world literature) as an undergraduate, I would now like to concentrate on English and American literature. I am especially interested in nineteenth-century literature, women's literature, Anglo-Saxon poetry, and folklore and folk literature. My personal literary projects have involved some combination of these subjects.” 

Again, this example shows what you should not do. This opening will not inspire confidence in readers, because it suggests a certain flightiness. Remember that readers want to see evidence that your experiences and skills have prepared you for graduate study. This statement suggests its author simply wants to take more undergraduate courses; what’s worse, he announces his lack of preparation to pursue the (five!) overly broad specialties he names.