Your personal statement gives you an opportunity to promote yourself and your achievements. Include interests and hobbies. You could also talk about your favourite subject and careers aspirations. This should make you sound as good as you can be, so don't put anything negative - but be honest at the same time!
Remember use a word processor or similar, using the spell-check facility, and copy and paste over when you're ready. And more is better, so try and fill in at least 240 characters.