Use examples to show your interest in how the Law actually works - and what you think about this. It can be an example from the news (ie. a current legal issue) or something more general that interests you. Explain your interest and why this issue is important to you.
If you have done any observation of Court Cases then mention anything that surprised you about this or something important you saw/learnt. This shows 'engagement' and genuine interest rather than 'my parents think I should do Law'.
Law Schools also like 'interesting people' - briefly explain any activities you do outside school, especially if you can show what you have learnt/gained from it - ie. working in a charity shop (experience with people outside your normal circle), running a 5k fun-run (working to deadlines, enthusiasm for a task, community spirit).