This is the part of the admissions packet where you are not just a number. Take advantage of this opportunity to state your case for admission to law school. See this guide for advice on how to proceed.
You should think of the personal statement as your opportunity to present that side of yourself that would come through in an interview. Although you should not gush uncontrollably about yourself, you should emphasize the events in your life that influenced you as a person and drew you to the study of law. Examples of topics most often addressed in statements include: selection of major, work or internship experience, obstacles overcome, educational background, motivation for the study of law, effect of disadvantage, family background, outstanding academic accomplishments, or significant extracurricular experiences. Remember to emphasize those things that will distinguish you from other candidates (e.g., significant employment, travel abroad, research projects, publication). Sell yourself.
Never emphasize defects in your record in the personal statement. If you want to explain a lower GPA or a low LSAT score, do so in a separate addendum. Be brief, factual, and honest.
Write in a direct, concrete fashion about real experiences, events, people and how they impacted you. Do not overuse adjectives and adverbs and do not use an abstract style. For example, if you mean "ball" say so; do not use the word "sphere" instead. Include anecdotal information to emphasize the point and make your statement more interesting to read. Do not, however, be cute. Essays that begin with a cliche -- such as, "If you were to look at my life, you would say it was an onion, each layer revealing my progressive individual development..." (this is an actual example) -- will turn the reader off.
How you write is as important as what you say. Do not turn in an essay that has not been proofread carefully. It is often helpful to read each sentence out loud to see if it sounds right. You should also carefully examine each paragraph to ensure that you are speaking to one particular topic or theme in each paragraph. Do not make a reader figure things out on their own or infer anything. Paragraphs in which critical information is not easily found are given very little if any further attention during the sometimes rapid reading accorded applications. Be sure to use separate paragraphs in order to signify transition from one topic to the next. Be clear, organized and reader friendly.
Limit yourself to around two double-spaced pages. A little over or under does not matter so long as you are being concise. Have a pre-law advisor or another trusted advisor review your personal statement.
Remember, the LSAT and undergraduate grade point average form the foundation of the admission evaluation process. A well-written personal statement might make an otherwise unimpressed admissions committee take another look.
For a few of examples of effective personal statements, take a look at these sample essays.