I wrote my personal statement a few months ago (last October) and found the most important aspect to be getting a correct, smooth, easy to read structure and then giving your own ass a good old kiss
I applied to do undergraduate German at 6 universites and have so far been accepted by 5, and I think writing, what I thought, was a good personal statement has really contributed.
My structure was:
1. I gave my reasons for choosing German and stated why I would like to continue studying the subject.
2. I mentioned my other A level courses and stated why I thought they had been of use and what skills I had aquired through these subjects.
3. Work Experience I had done.
4. Volunteer Work, my involvement in Amnesty International, Part time jobs. (You could replace this with any other good cause you have ever been involved with) Its important to get across that you believe in what you have done and how it reflects on you as a person.
5. Sports/Reading. I mentioned that I play tennis and enjoy reading (buffing it out with sentences such as 'I believe that a solo sport such as tennis, which requires much discipline, thought and self belief can be beneficial in gaining skills that are of particular use during examination periods, having self control is vital in times of pressure.' Kind of over the top Lol)
6. (conclusion) 'My defining qualities as a person, yet more importantly as a student are...' I then carried on from there and wrote about why I would be an asset and of my other qualities. Remember not to beg, i.e It would be an absolute priviledge to..., especially if you believe that you should be accepted to the universities that you have applied for. Make them want you, tell them why they should really want you at their university.
This was my plan and you may have other ideas, which is probably the best way to go, but try and keep your statement well structured. I read several statements and often people had failed to do this, and had made their statement very unorganised by putting sentences, which should have been lumped into one seperate paragraph, all over the page.