It is important to cover whatever period you intend to include in your personal statement because time spent planning your sequence and the method you feel happiest with will undoubtedly make the actual writing that much easier for you.
3 _ Demonstrate ambition _ What is your end goal? Do you want to become a solicitor or a barrister? Do you want to study law as an academic? Or do you want to go into law for the great skills it teaches you? Law schools will want to to know where your end goal lies. If you have your heart set on becoming a solicitor, and this passion comes across in your personal statement, it shows a great drive to succeed. And that's obviously something which will be beneficial during your degree.