Read over the requirements of each college and carefully think over your life experiences to pick the one that will best help you meet the personal statement guidelines. Don't just write up a generic statement that you plan to send to every college.
Pick a topic about which you are passionate. Your essay will be one of many that the admissions committee will read, so it needs to be interesting and well-written. If you play it safe and select a subject that bores you, you will more than likely end up boring the committee as well.
Do not write solely about your academic achievements, especially if they are already detailed in other parts of your application. Use the personal statement to highlight the things that make you special that won't be revealed by your GPA or SAT score.
College admissions officers want to read personal statements that are well-written, use correct grammar and punctuation, and reveal something to the committee that it didn't already know about the applicant.
The committee will also be looking to see if you have done your homework for certain types of personal statements. For instance, if you are answering the question "Why do you want to go to this college?," don't answer in generalities. "I love John Doe University because the students look so happy" will not cut it. Instead, use specifics about things you've learned about the college and the degree want to obtain.
To avoid rambling, don't pick a subject that is overbroad. If, for instance, you decide to write about a life-changing mission trip, don't include everything from the time you left for your flight to the second you returned home. Instead, focus on an event that reflects why the trip was important to you, and use vivid detail and the active voice to engage the reader.
One of the hardest things to do in a personal statement is to show the college what makes you special without appearing egotistical or obnoxious. Read your statement over to look for areas where you might be exaggerating or are bragging too much.
Proofread your finished statement carefully, reading it for grammatical and spelling errors. Read it again to make sure it makes sense and answers the question asked. Have at least one other person -- preferably someone with good editing or writing skills -- read your statement over for errors. Listen with an open mind to his criticism; if you don't agree, get a second opinion. Check that you have kept your personal statement within the word count guidelines.