Start somewhere. The most difficult part about writing a personal statement is starting. Begin by brainstorming about the unique and interesting things that have happened to you and that will interest your audience. Write these down, and don't worry if it makes sense. Jog your memory by asking yourself questions like, "What accomplishment am I proudest of?" "What is the most difficult challenge I have faced and how did I overcome it?" "What makes me different?" Ask a friend to help you answer some of these questions; other people tend to see more uniqueness in us than we do in ourselves.
Find other sample personal statements. The best sample personal statements for you will be successful personal statements written for the program, field, scholarship, or fellowship to which you are applying. By looking at those sample statements you will be able to see what selection committees of the various organizations tend to respond most to, and what other successful applicants have emphasized in their personal statements. Find them by contacting the relevant program administrator or your school's financial aid or scholarship office. You can also conduct a library search with the help of a librarian, or look online for samples.
Construct your own narrative. Once you have chosen a sample, do not feel like you have to follow it religiously. It should only serve as a guide, and help you see a way of bringing together your own professional story. Think about what parts of your brainstorming exercise fit into a cohesive narrative, and discard the ones that do not, no matter how cute or funny you think they might be. Stories about dreams and aspirations one has had from an early age are rarely, if ever, effective in a personal statement because they do not have much persuasive power.
Focus on quantifiable attributes. Make sure you discuss actions or changes that you made that are visible and tangible. Even if you want to say that you realized something was wrong or missing from your professional or personal life, follow it up immediately with an action you took to correct it. Try to stay away from words like "felt" and "thought" because they do not convey much conviction.
Have multiple readers look over your statement. Find expert readers who are informed about what a personal statement is supposed to be -- teachers, professors, writing center instructors, and other educators. Your friends and family may be well-meaning but unless they are well-versed in writing personal statements, they may not give you the kind of advice that will help you write a better statement.
Revise your draft. You should expect to revise your personal statement multiple times before you submit it. There is no rule of thumb as to how many revisions you should make, but personal statements are so individualistic and the stakes for writing them often high enough that they take most people many more revisions than their usual number to perfect. At the end of your revisions your personal statement will have likely taken on a life of its own and may look very different from the sample personal statement you used as a template.