Keep the following in mind when you write your essay:
1. Limit your essay to 350-500 words.
2. Describe an event that shaped your beliefs or a person who inspired them.
3. Avoid sermons and editorials—no soapbox declamations, please!
4. Read more of the This I Believe essay-writing tips.
You can peruse multiple examples at http://thisibelieve.org. Often the ones put on the radio are a bit better, but not necessarily so.
Andrea Kang's (Class of 2009) This I Believe essay. They re-posted it from its original posting so all of the comments are gone, but her essay is there.