The most important thing is to be sincere! Admissions folks read thousands of applications each year, and they can quickly tell which applicants are trying too hard to be impressive. For example, do something you like for your extracurricular activities--if you want to spend your time volunteering at a pet shelter instead of running track, go for it! For your personal statement, tell a story that matters to you, even if you feel like it is not "cool" or "important" enough. People want to see students who are engaged and have a diversity of interests. Your personality will shine through when you do and write about things that matter to you.
And, like Norma said, you should also make sure to demonstrate interest! Spend time researching each school you are applying to, and tailor your personal statement to show that you are interested in that school.
Best of luck!